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The PCB Design Resource Channel is a worthwhile location that provides electronic engineers and designers with top-notch resources and tools to design printed circuit boards. In this section, the latest guides in design, tutorial videos, software tools, example projects, and best practices are organized together for reference on how best to go about optimizing the design process for better work efficiency and product quality.

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PCBA Resources - PCB Expert Manufacturing - PCBX

Thermocouples are very vital in modern electronics, serving as good temperature sensors in many applications. Their integration into PCBs is crucial, especially in fields where thermal profiling and management need to be critically addressed, such as in SMT assembly. This article outlines the best practices for attaching a thermocouple to a PCB, ensuring accuracy and dependability in temperature measurement.A thermocouple is a temperature sensor made from two dissimilar metal wires joined at one end. As the junction undergoes a change in temperature, a voltage proportional to that change is produced, thus enabling precise temperature measurements over a wide range. In addition, thermocouples are applied in many cases because of their strength, inexpensiveness, and capability of working within extensive ranges of temperatures.In the context of PCBs, thermocouples provide true real-time temperature monitoring during a critical process such as soldering and thermal cycling with feedback that is essential for ensuring component integrity and performance.<img src="https://img.pcbx.com/dev/file/image/article/20241217/694f1d8314bc47658d1803552dc7a134.jpg" alt="How to Attach a Thermocouple to a PCB-PCBX" data-href="" style="width: 100%;"/><h3>How to Attach a Thermocouple to a PCB</h3>Following are several methods for mounting a thermocouple in place on a PCB, based on the advantages and the application considerations.High-Temperature Soldering: High-temperature solder is used to solder the thermocouple directly onto the PCB. Soldering provides a very stable and durable connection, suitable for applications that undergo many thermal cycles. However, great care must be taken in order not to damage the PCB, and a good thermally conductive joint is difficult to realize. This method is generally used where high reliability is of prime importance, although this method is time-consuming and requires precision.Aluminum and Kapton Tape: The aluminum and Kapton Tape provide a non-destructive alternative. In this easy-to-apply-and-remove technique, which does not leave any damage or residue, the thermocouple is held down with Kapton tape onto aluminum tape used for thermal conductivity. This method applies in a variety of scenarios and, though quite versatile, tends to be less reliable when it is under severe thermal stress. This is applicable where the test needs flexibility without causing permanent changes to the PCB.Epoxy Adhesives: Which are two-part adhesive systems used to attach a thermocouple to a PCB with a strong bond. These are especially useful in applications where tapes cannot be used due to space constraints. Epoxy adhesives form strong bonds. However, these bonds tend to deteriorate with time by repeated thermal cycling, hence long-term thermal exposure.Kapton Tape Alone: Kapton Tape relies exclusively on the excellent thermal insulating properties of Kapton tape to secure the thermocouple to the PCB. Cost-effective and straightforward, this can be considered an ideal method where the thermal environment is less demanding. In extreme thermal conditions, however, reliability may suffer as the adhesion properties of the tape degrade.<h3>Reliability Evaluation of Attachment Methods</h3>High-temperature soldering, though considered the most reliable method of attaching thermocouples robustly and precisely, has practical alternatives like aluminum tape and epoxy for attachments in scenarios where high precision is not the chief concern. These alternative methods also provide flexibility and ease of application that minimize potential stress to the PCB and allow straightforward modification if the need arises. <h3>Importance of Proper Attachment for Accurate Measurement</h3>Accurately attaching thermocouples to a PCB is crucial for correct thermal profiling. If installed correctly, temperature readings will reflect the actual temperatures of the surface of the PCB rather than the ambient air, which can be quite different. This is important to prevent thermal shock to sensitive components during SMT reflow processes.<h3>Choosing the Right Thermocouple</h3>Selection of the correct thermocouple is rather more than just choosing from a temperature range. In fact, other factors exist, including response time, environmental resistance, and material compatibility. The K-type thermocouple is pretty common owing to its broad temperature range and good report on reliability.<h3>Additional Considerations</h3>Calibration: Thermocouples should be calibrated according to the industry's standards to provide an exact measurement.Environmental Adaptation: If there is an application in corrosive or challenging environments, protective means must be introduced.Signal Conditioning: Include mechanisms to amplify thermocouple output for improving measurement sensitivity even in very noisy environments.<img src="https://img.pcbx.com/dev/file/image/article/20241126/b02f1286181b4540b3889318b8d2d53a.jpg" alt="How to Attach a Thermocouple to a PCB-PCBX" data-href="" style="width: 100%;"/>Thermocouple attachment to a PCB is one of the precision tasks that holds the key to success for any thermal management of an electronic assembly. Application and environment determine the correct attachment method, whether it is through high-temperature soldering, tapes, or adhesives.Each technique has its own advantages and disadvantages, which further calls for great care while incorporating these methods for accurate and reliable temperature monitoring. Appropriately attached thermocouples mean that the devices will operate within safe thermal parameters and thus enhance the efficiency and longevity of electronic products.

Thermocouples in PCBs ensure accurate temperature monitoring; attach with solder, tapes, or epoxy based on application needs for effective thermal management.

How to Attach a Thermocouple to a PCB

Among the generally fabricated printed circuit boards, Black FR4, otherwise known as "Black Core," has been able to create a special niche in the world of printed circuit board fabrication due to peculiar aesthetic and functional advantages. This special sort of FR4 PCBs features a black substrate that distinguishes it from conventional FR4 circuit boards. The paper throws light on the characteristics, advantages, and applications of black core PCB along with key considerations in designing them.<h3>What is a Black FR4 PCB?</h3>A Black FR4 PCB is a special kind of printed circuit board made on an FR4 substrate dyed black. "FR4" refers to a fire-resistant fiberglass-reinforced epoxy laminate material. The black core look and feel are what differentiates these PCBs from regular green or other colored FR4 boards, popular in electronics manufacturing when aesthetics is a factor.<h3>Why Use Black Core PCBs?</h3>Black core PCBs are not used just for cosmetic reasons, functional properties prevail, too. Here are a few things that they can deliver :Light Blocking CapabilitiesWhere there is a component or sensor sensitive to light interference in the application, it should be completely avoided. Yes, the black solder mask is light-blocking; however, only black FR4 would provide complete opacity and remove chances of light seepage through the circuit board.Appealing LooksBlack PCB boards give an aesthetic look and a graceful appearance that every consumer of electronic devices wants. The black surface further masks the traces of copper, giving it a far more professional look. This is just what top-of-the-line product design requires.<img src="https://img.pcbx.com/dev/file/image/article/20241101/66add085a39d43c6b5e239b2d0930024.jpg" alt="Black FR4（Black core) PCB-PCBX" data-href="" style="width: 100%;"/><h3>Features of the Black Core PCB</h3>Excellent Heat Dissipation: The thermal conductive substrate of the black circuit boards has an outstanding heat dissipating capacity. It reduces the working temperature of circuit components, improves system reliability, and is appropriate for high-power applications with heat sensitivity.Durability and Longevity: Resilience: Unlike traditional materials, black FR4 boards are highly strong and resistant to temperature fluctuations. This helps equipment to last longer while reducing maintenance and replacement costs.Enhanced Signal Performance: Because of its low dielectric constant and dissipation factor, black core FR4 PCB boards have lower signal attenuation and distortion, resulting in improved signal transmission.The luring black finish of the black PCB boards enhances the aesthetic quality of the device. That eventually is helpful for the designs that require modern and stylish looks, as black blends with a lot of component and casing colors.<h3>Considerations for Black Core PCB Design</h3>Thermal ManagementThis is because the components made of black core material have excellent dissipation properties, and thermal management needs to be proper. Only when the working temperature range of the PCB falls in the safe zone is it assured that the performance and life of the circuit are taken care of.Material CompatibilityThe black core FR4 should be compatible with other materials and components used on the board for its reliability; otherwise, incompatibility can create instability in the boards and also short life.Signal StabilityMost naturally, the properties of the black FR4 circuit board provide a shield for signal stability and address the problems of heating while the transmission of the signals is going on. Proper design would do well to take into consideration thermal interference to ensure that communication goes through without hindrances.Uniform Power DistributionEnsure uniform power distribution across the PCB to prevent voltage fluctuations from disrupting the circuit's functionality.&lt;button class="center btn-lg" data-href="/order/manufacturing/pcb"&gt;Get an Instant Quote for Black FR4 PCB Manufacturing&lt;/button&gt;<h3>Applications for Black Core PCBs</h3>Automotive Electronics: Features include infotainment systems, dashboard controls, and innovative driver assistance systems that combine functionality and aesthetic appeal.Consumer Electronics: Esthetics and functionality need to be supported, for example, on high-end audio devices, smartphones, and wearables.LED Lighting: The contrast in the visual effect of the lighting applications is enhanced by the LED system, and the reflection of light is also improved.Industrial Control: They can be applied to automation and machinery control systems since they are stable enough in these arduous environments.Gaming and Entertainment: Black PCBs are also aesthetically good-looking for game consoles and entertainment systems to ensure a better user experience in them.<img src="https://img.pcbx.com/dev/file/image/article/20241101/01227f4977d048c5837a7ed8027c1d09.jpg" alt="Black FR4（Black core) PCB-PCBX" data-href="" style="width: 100%;"/>Black core PCBs normally rely on aesthetic considerations and particular design needs, yet they function just like ordinary FR4 PCBs. By embedding black core PCB in your design, you will be able to achieve technical precision with aesthetic appeal for a quality output product over several electrical applications.

Black FR4 PCBs offer aesthetic and functional benefits, including light blocking, heat dissipation, and enhanced signal performance, suitable for electronics.

Black FR4（Black Core) PCB

Understanding ENEPIG in PCB Manufacturing

Printed Circuit Boards form the backbone of modern electronics, right from mass consumer gadgets to critical systems in space. As electronic devices forge ahead with developments, the need for reliable and efficient PCB surface finishes has become a general requirement. Among the different options for the same, ENEPIG stands out, which goes by the name of Electroless Nickel Electroless Palladium Immersion Gold, owing to its exemplary performance attributes. The article is a how-to guide discussing what makes ENEPIG better for high-performance PCBs and compares it to other finishes such as ENIG, which stands for Electroless Nickel Immersion Gold.<h3>What is ENEPIG?</h3>ENEPIG is a multi-layer, complicated coating on PCBs. It allows for superior corrosion resistance, solderability, and capabilities of wire bonding. The three layers are deposited one after another on top of each other, namely nickel, palladium, and gold. Each of these performs a different function:Nickel Layer: Laid electrolessly, as the first layer, nickel prevents the diffusion of copper and provides a sound base for the succeeding layers. The thickness normally ranges from 3 to 6 microns.Palladium Layer: Palladium is a thin layer laid over the nickel layer, with a thickness ranging between 0.05 to 0.2 microns. It exhibits outstanding resistance to corrosion and protects the nickel layer against oxidation and prepares it for the deposition of gold.Gold Layer: Outermost 0.03 to 0.1 micron immersed plated layer that prevents oxidation and allows for very good solderability for attaching components onto the board.<img src="https://img.pcbx.com/dev/file/image/article/20241017/28d38b61dcd646f78aa3fa1613b598df.jpg" alt="ENEPIG-PCBX" data-href="" style="width: 100%;"/><h3>How ENEPIG Works</h3>The ENEPIG manufacturing process is primarily a process called electroless deposition, which consists of no external power source. In fact, this method is inherently robust and reliable and ensures that the layer thickness is uniform over the PCB. The major stages of the process involved in manufacturing for ENEPIG are mentioned below:Copper Activation: One of the most important steps in the adhesive properties of the nickel layer is the treatment of the copper surface. Cleaning or etching of the copper removes contaminants and oxides, thus providing an optimum substrate for plating.Electroless Nickel Plating: Deposit a layer of nickel on the activated copper. Such a layer would serve as a barrier to prevent copper migration and offer a stable substrate for deposition of the palladium and gold layers.Electroless Palladium Plating: The second layer is palladium, a corrosion-resistant metal. This layer is very crucial, as it enhances finish durability and proper adhesion of gold effectively.Gold Immersion Plating: The gold improves solderability by preventing oxidation with the additional gold layer. It is used to coat PCBs reliably to enable assembly and long-term performance.<h3>ENEPIG Advantages</h3>Improved Solderability: The gold layer in ENEPIG allows for better solderability and thus finds applications in high-reliability markets where consistent and strong solder joints are required.Excellent Corrosion Resistance: The corrosion resistance is radically improved with a palladium buffer layer protecting the nickel, thus assuring long life even in very harsh environments.Improved Wire Bonding: ENEPIG is compatible with both gold and aluminum wire bonding, thus extending its applicability for a wide range of assembly requirements, from simple to very stringent, such as in aerospace and telecommunications.Low Contact Resistivity: The multilayer composition of ENEPIG provides very low contact resistivity, hence extending its usage into RF and microwave applications where high-frequency performance is required.<h3>Limitations of ENEPIG</h3>While ENEPIG indeed boasts many advantages, it is by no means perfect:Higher Cost: ENEPIG includes palladium, making it more expensive than simple finishes such as ENIG. Additional material and processing costs come with the extra layer.Complex Manufacturing Process: ENEPIG is a multistep process that is painfully precise in nature. The increased lead times in manufacturing and added complexity versus single-layer finishes make it challenging.Limited Availability: Not all manufacturers are equipped to make ENEPIG. This creates possible supply chain constraints of ENEPIG, particularly in smaller lots.<h3>ENEPIG vs. ENIG</h3><img src="https://img.pcbx.com/dev/file/image/article/20241017/9a192123e7c843d9804ecaf1ba92ac7b.png" alt="ENEPIG vs. ENIG-PCBX" data-href="" style="width: 100%;"/>Cost: More expensive due to the added layer of palladium, while the general cost of ENIG is lower but will not give up much in performance for the more budget-conscious job.Solderability: Both feature great solderability, but ENEPIG offers consistent and reliable joints due to its multi-layer structure.Corrosion Resistance: ENEPIG certainly shows greater corrosion resistance with the inclusion of the palladium layer; ENIG may not be quite as robust in extreme conditions.Wire Bonding: ENEPIG has the advantage of gold and aluminum wire bonding, but ENIG is confined to gold wires.<h3>Applications of ENEPIG</h3>High-Reliability Applications: In industries that have no margin for errors-aerospace, medical devices, and telecommunications-ENEPiG tops the list among all other metals.Automotive Electronics: Since ENEPIG is capable of withstanding immense pressure, this material is suitable for ADAS and engine control units.RF and Microwave Circuits: ENEPIG, with its ultra-low contact resistance, is especially suited for very high-frequency applications because it ensures good data transmission in telecom infrastructure.<h3>Conclusion</h3>ENEPIG represents the epitome of surface technology on printed circuit boards. Its unrivaled reliability, performance, and versatility bestow special status upon it among other finishes. Higher costs and manufacturing complexity notwithstanding, its advantages often justify the investment required, especially for high-stakes applications. ENEPIG is an optimum solution for industries requiring strong and reliable PCBs, enhancing functionality and the life expectancy of electronic assemblies. Being one of the most popular choices among high-tier surface finishes, ENEPIG continues to raise the bar high in the production of PCBs and, therefore, becomes a decent option to consider for your next high-performance project.

ENEPIG is a high-performance PCB finish with nickel, palladium, and gold layers, offering superior solderability, corrosion resistance, and wire bonding for critical industries like aerospace and telecom.

A Solder Mask, also known as Solder Resist, consists of a layer of polymer material applied on the surface of a Printed Circuit Board-PCB. This coating is applied to protect a PCB against potential oxidation apart from avoiding any accidental solder bridges between adjacent traces while performing the soldering process. Solder mask usually comes after the copper traces and vias have been etched and solder pads have been plated. Materials commonly used for solder mask include thermoset epoxy and liquid photoimageable (LPI) solder mask. It is applied in such a pattern that the copper pads and vias, which are to be soldered, expose, while the rest of the places-which are not to be soldered-are called "lands".<img src="https://img.pcbx.com/dev/file/image/article/20240920/88b618dc8eb9464fb3e0a676fbb55b59.jpg" alt="solder mask-PCBX" data-href="" style="width: 100%;"/><h2>Purposes of Solder Mask</h2>Solder masks are applied on top of the solder side of a PCB. Their major functions include:Protection: The mask covers the copper traces from oxidation and corrosion due to environmental factors, hence enhancing the durability and reliability of a PCB.Insulation: The solder mask insulates the adjacent copper traces from each other, hence preventing the possibilities of short circuits from mislaid solder or other kinds of contamination.Solder Bridging Prevention: It avoids the possibility of solder sticking to wrong places of the PCB, hence avoiding solder bridges that would present electrical faults.Aesthetic Appeal: The solder mask helps the PCB present a uniform, professional appearance, making some aspects of visual inspection easier. Various colors can also be applied for branding purposes or differentiating between different types of PCB.<h2>Common Types of Solder Masks</h2>Below is an overview of the three most common types of solder mask and their respective advantages and disadvantages:<h3>Liquid Photoimageable, or LPI, Solder Mask</h3>LPI is the most commonly used type of solder mask. Applied as a liquid, LPI is exposed to ultraviolet light for hardening.Pros: High resolution; hence, suitable for fine features and high-density PCBs. Color: Available in wide range.Cons: More expensive than other types and UV light is required for its cure.<h3>Dry Film Solder Mask</h3>Dry film solder masks are processed by applying pre-made film onto the PCB, followed by lamination and curing. Normally used in high temperatures for automotive or aerospace electronics-based applications.Pros: Provide good chemical and mechanical resistance; best suited for use in high-temperature applications.Cons: Limited colour options; not suitable for fine features.<h3>Epoxy Liquid Solder Mask</h3>Epoxy solder masks are applied as a liquid and then cured with heat. They can be found in applications that require a great deal of durability, such as industrial control systems and medical equipment.Pros: It provides very good adhesion, with excellent mechanical strength; thus, suitable for durable applications.Cons: Colour limitation and perhaps more difficult to apply compared with other types.<img src="https://img.pcbx.com/dev/file/image/article/20240920/48631d45bdb44a7eaec9558aa626ae6b.jpg" alt="solder mask-PCBX" data-href="" style="width: 100%;"/><h2>Selection Factors for Solder Mask</h2>In choosing solder mask for a given PCB, a number of factors need to be put into consideration and these include:PCB Design: High-density PCBs would require solder masks with high accuracy and resolution such as LPI.Application: The PCB application will drive the selection of solder mask because it could be in mechanical or even at high temperatures.Cost: It can be determined by budget in some cases because not all solder masks are equally expensive.Color: Tend to vary depending on the differentiation of PCB components or depending on aesthetic requirements.<h2>How to Apply Solder Mask on a Printed Circuit Board</h2>The application of solder mask would normally involve several steps for it to be able to work effectively: Cleaning and Preparation: Thorough cleaning is carried out on a PCB to ensure that there is no kind of contamination that can prevent solder mask adhesion.Solder Mask Application: Some of the common techniques used in this process are screen printing, spray coating, or inkjet printing, but by far, the most used technique is screen printing.Solder Mask Curing: Allow applied solder mask to cure under either heat or UV light; it hardens and provides good adhesion.Inspection of PCBs: Inspect the PCBs for defects such as incomplete coverage. Any noted issues will need repair before further processing of the PCB.Proper application and curing of the solder mask is thus essential to a reliable operating PCB.<h2>Conclusion</h2>Solder masks play a major role in the manufacture of PCBs for protection, insulation, and aesthetic reasons. The type of solder mask that will be used would depend on the design of the printed circuit board, its operating environment, and the budget allocated for that particular product. Being able to understand the types and their respective advantages is helpful in making informed decisions about the reliability and performance of the final product. A solder mask applied and cured well really enhances quality and durability in PCBs, which become important in different high-demanding industries.

Solder mask, or solder resist, is the polymer layer on PCBs that protects against oxidation, short circuits, and solder bridges. Types include LPI, dry film, and epoxy, chosen based on design, application, and cost.

What is Solder Mask?

Copper is used for conducting routes on printed circuit boards (PCBs) because of its excellent electrical conductivity and strong physical characteristics. Unfortunately, copper is highly reactive and oxidizes quickly in air to form a thin solid oxide layer at the surface, which cause defects in the solder joints and hence reliability issues with the product, thereby reducing the life of a product. Therefore, protection from copper oxidation is essential. This requirement has brought about several surface coatings, which should withstand heat and be solderable. This article explains the functions, types, and principles of selection of surface coating on PCBs.<h2>What is PCB Surface Coating?</h2><h3 style="text-align: left;">Why PCB Surface Coating is Important？</h3>These surface finishes are applied to the copper pads of a PCB to prevent oxidation and contamination while retaining solderability. Copper is an excellent conductor and inexpensive; hence it is used as a conducting material for PCBs. Its high degree of reactivity means it easily forms an oxide layer, leading to defects in the solder joints and significantly reducing the reliability and shelf life of the product.Statistics indicate that about 70% of the defects in a PCB are due to solder joints, and there are two major reasons for this:Oxidization and Contamination: Oxidation and contamination of the pads on a printed circuit board will lead to incomplete soldering or cold solder joints.Diffusion and Inter-Metallic Compounds (IMCs): Diffusion between silver and copper, and the formation of IMCs between tin and copper at the interface, make it loose and brittle.Hence, a solderability or isolation protective layer on the copper surface is necessary to reduce or prevent these defects.<h3 style="text-align: left;">Requirements for PCB Surface Coatings</h3>The following are the characteristics desired of the surface coating on a PCB pad:Heat ResistanceThe coating needs to prevent the oxidation of the surface of the PCB pad during high-temperature soldering and enable solder reverse contact to take place with copper directly. The melting point of the coating should be close to or lower than that of solder, while its thermal decomposition temperature is much higher.CoverageThe coating shall provide good coverage of the copper pad surface such that no oxidation or contamination at all may occur before and during soldering. It should also not drift, decompose, or float on the solder joints and represent all solder adhesion onto the pad.ResidueThe residue left on either the pad or solder joints after soldering should be kept as minimal and easily removable to prevent any potential kind of hazard.CorrosivityThe coating should not cause corrosion of the substrate or metallic layers of the PCB during the post-soldering process.Environmental ConsiderationsEnvironmental consideration is gaining much importance. The effluents generated during application and related cleaning processes should have easy handling and be ecologically friendly.<h2>Types of PCB Surface Coatings</h2><h3 style="text-align: left;">Based on Manufacturing Technology</h3>The PCB surface finishes depend on their manufacturing processes, and according to this, including:Surface CoatingPhysically adds a thin, heat-resistant, and solderable coating to the copper surface. Examples include HASL and OSP.<table style="width: auto;"><tbody><tr><th colSpan="1" rowSpan="1" width="auto"><img src="https://img.pcbx.com/dev/file/image/article/20240821/7b473552805c484084887d43aa7a61ea.png" alt="HASL-PCBX" data-href="" style=""/></th><th colSpan="1" rowSpan="1" width="auto"><img src="https://img.pcbx.com/dev/file/image/article/20240821/7ea3f34eec5845498f49956d877190c4.png" alt="OSP Finish-PCBX" data-href="" style=""/></th></tr></tbody></table>Metal CoatingConsists of electroless plating and electroplating to create a metal coating over the copper pad, which is heat-resistant and solderable. Examples include ENIG and ENEPIG.<img src="https://img.pcbx.com/dev/file/image/article/20240821/c603e1ca99cd445e99fcf6dbbf61b4cf.png" alt="ENIG and ENEPIG-PCBX" data-href="" style="width: 100%;"/><h3 style="text-align: left;">Based on Application Effects</h3>According to their application effects, the surface finishes can be divided into three categories as follows:Soldering flux on the coating of the isolating layerAllows the solder to float on the surface under high-temperature soldering; however, IMCs can form at the interface, increasing defect risks.Soldering flux on the metal coating of the diffusion layerDesigned to eliminate IMCs but can cause diffusion and brittleness, which may result in defects in circuits.Soldering flux on the isolating layer of the metal coatingAvoid the contact of solder with copper and hence it will not form any IMC or normally diffuse the metal, thus providing an increase in reliability to the part.<h2>Choosing the Correct Type of PCB Surface Coating</h2>This PCB surface coating selection may have an impact on solderability, reliability, and shelf life. The decision is based on the application and its requirements.<h3>For a General Application</h3>Coatings like HASL or OSP, which allow soldering flux to adhere without an isolating layer, are appropriate for use in consumer electronics and industrial devices.<h3>For High-Reliability Applications</h3>In high-reliability and long shelf life applications, it is recommended to use surface coatings in which the soldering flux adheres to an isolating layer itself, like ENIG or ENEPIG, in fields of medical devices, transportation, military, and aerospace.Knowing the importance, types, and selection criteria for PCB surface coatings will significantly improve the quality and reliability of products in a variety of industries.

Copper in PCBs oxidizes, causing solder defects and reducing product life. Surface coatings like HASL, OSP, ENIG, and ENEPIG prevent this, ensuring solderability and reliability. Choosing the right coating based on application needs significantly improves the quality, reliability, and lifespan of products.

PCB Surface Coating Functions and Selection Principles

While designing or ordering a printed circuit board, have you wondered if the silkscreen layer was really necessary, and if so, at what extra cost? Let's see what a silkscreen is and why it's important in PCB manufacturing.<h4>What is Silkscreen?</h4>Applied on the PCB for identification purposes is the silkscreen, otherwise known as the layer of non-conductive ink: components, test points, parts, warning symbols, logos, and other markings. Normally, this should be applied to the component side, but sometimes this is placed on the solder side of the board. A more detailed silkscreen will help the manufacturer and the engineer locate where all the components of a PCB will be placed.This layer uses epoxy ink, normally black, white, or yellow, and most PCB software uses standard fonts for these markings. Conventionally, silk-screening would require the following tools: a polyester screen stretched on aluminum frames, a laser photo plotter, a spray developer, and curing ovens.The silkscreen layer can include important information, such as:<ul><li style="text-align: left;">Polarities of parts</li><li style="text-align: left;">Location of parts through reference designators</li><li style="text-align: left;">Test points</li><li style="text-align: left;">Unique identification numbers for each board</li><li style="text-align: left;">Warning symbols.</li></ul><img src="https://img.pcbx.com/dev/file/image/article/20240821/18578b066b4a42f287f748ac39474b28.png" alt="pcb silkscreen-PCBX" data-href="" style="width: 100%;"><h4>The Importance of Silkscreen in PCB Assembly</h4>In the past few years, silkscreen applications have undergone a shift from the use of stencils to direct application methods. Currently, there exist two major methods which are applied in the printing of silkscreen on a PCB. These are liquid photo imaging and direct legend print.<ul><li style="text-align: left;">Liquid Photo Imaging (LPI): Using line widths greater than 4 mil, liquid photo-imageable epoxy is coated onto the laminate and exposed with UV light, then developed and cured on the board, providing increased accuracy compared to manual screening.</li><li style="text-align: left;">Direct Legend Printing (DLP): This offers the highest accuracy at a higher cost. The inkjet projector sprays acrylic ink onto the raw PCB guided by CAD data, and UV light cures the ink as it comes out from the printer. Note that acrylic ink does not cure well on boards finished with silver.</li></ul>While silkscreen application happens during fabrication, it is extremely important for assembly, which involves component placement or mounting. Some key silkscreen markings that facilitate proper placement include:<ul><li style="text-align: left;">Reference Indicators: Explains what kind of components are from the BOM.</li><li style="text-align: left;">Pin 1 Indicators: Shows which pins connect to what pads of the footprint.</li><li style="text-align: left;">Component Outlines: Combined with the landing pattern, these indicate where the components should be placed.</li><li style="text-align: left;">Polarity Indicators: Indicate the orientation of polarized components.</li></ul>For parts with few pads or simple shapes, omission of the component outline for general placement may be acceptable. It will then create asymmetrical placement issues, such as tombstoning, in soldering. The absence of reference, Pin 1, and polarity indicators can make a component be oriented or placed incorrectly. This would then lead to poor device functionality.&lt;button class="center btn-lg" data-href="/order/manufacturing/pcba"&gt;Get an Instant Quote for PCB Assembly&lt;/button&gt;<h4>PCBX's expertise in silkscreen</h4>PCBX has become one of the most experienced manufacturers for PCBs and PCB assembly in China, having been an industry leader for almost two decades. PCBX specializes in quick-turn PCB prototypes and assembly, as well as medium and small volume PCB manufacturing, and strives to satisfy all of your silkscreen requirements with high quality and precision on every project. Cooperating with PCBX will provide you access to our expertise and dedication to superior silkscreen application on your PCBs.

The silkscreen layer, made of non-conductive ink, is vital for identifying PCB components and ensuring accurate placement. Methods like Liquid Photo Imaging and Direct Legend Print enhance precision. PCBX excels in producing high-quality silkscreen applications, crucial for proper assembly and functionality.

PCB Silkscreen

PCB Surface Finishes Introduction and Comparison

While ordering PCBs, one needs to decide upon the substrate material of the PCB, solder mask, silkscreen, surface finish, size and thickness of the board, the thickness of copper, blind and buried vias, through-hole plating, SMT, panels, tolerances, and any other specifications before your circuit boards are fabricated. Of these factors, the choice of surface finish is most important due to its large effect on the reliability of an electronic product. Since the copper layers on the PCBs are easily oxidized, this oxidation can seriously degrade soldering quality and hence the reliability or functionality of final products. The surface finish prevents the pads from oxidation, ensuring good solderability for electrical performance.Surface finish, known as surface coating, is an important process between <a href="https://www.pcbx.com/" target="_blank">PCB manufacturing</a> and <a href="https://www.pcbx.com/assembly" target="_blank">circuit board assembly</a>, offering dual functions in its processes: first the protection of exposed copper circuitry, and second solderability for component attachment. As seen in Figure 1, the surface finish is applied onto the outermost layer of the PCB on top of the copper, which functions like a protective "coat" for the copper.<img src="https://img.pcbx.com/dev/file/image/article/20240807/9bf3a4435f304628b1d5e5966e338521.png" alt="Surface Finish on PCB-PCBX" data-href="" style="width: 50%;"><h2>Types of surface finish</h2>There are mainly two big categories for surface finishes of a PCB: metallic and organic. Metallic finishes include HASL, ENIG/ENEPIG, Immersion Gold, and Immersion Tin, while OSP and Carbon Ink are under organic finishes.<h3>HASL Hot Air Solder Leveling</h3>HASL is the conventional surface finish, which is always applied to PCBs. In this process, the board is submerged in a bath of molten solder; this flow completely covers all the exposed copper surfaces with solder. This excess solder is removed by passing the board through hot air knives as shown in Figure 2 below：<img src="https://img.pcbx.com/dev/file/image/article/20240807/d39bec69331e4dff91741dbbf3df5db5.png" alt="HASL Process-PCBX" data-href="" style="width: 100%;"/><table style="width: auto;"><tbody><tr><td colspan="1" rowspan="1" width="auto" style="text-align: center;">Pros of HASL Surface Finish</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">Cons of HASL Surface Finish</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Excellent wetting during component soldering; • Copper corrosion avoided;</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Low planarity on vertical levelers leads HASL unacceptable for fine pitch components; • High thermal stress during process causes defects into circuit board; </td></tr></tbody></table>On account of concern for the protection of the environment, HASL itself has evolved into two variants: lead-based HASL and lead-free HASL. The lead-free version is compliant with RoHS regulations, first put in place by the EU.<h3>ENIG and ENEPIG</h3>ENIG is an abbreviation for Electroless Nickel Immersion Gold. A coating of electroless nickel is put on the PCB, followed by a small layer of immersion gold to keep the nickel from oxidizing. ENEPIG stands for Electroless Nickel Electroless Palladium Immersion Gold, which means that in addition to what ENIG does, a palladium layer will be added to act as a barrier, preventing nickel from oxidizing and diffusing into the copper layer. While ENIG and ENEPIG provide far improved solderability to the other surface treatments, their prices are significantly higher. The varied processes for creating ENIG versus ENEPIG are diagrammed below in Figure 3:<img src="https://img.pcbx.com/dev/file/image/article/20240807/760e7b88166040c9b4bab1769f243253.png" alt="manufacturing process of ENIG and ENEPIG-PCBX" data-href="" style="width: 100%;"/>The electroless nickel step is autocatalytic, a deposition of nickel onto the palladium-catalyzed copper surface. The reducing solution contains nickel ions, which must be maintained in specified concentrations, temperatures, and acid levels. During the Immersion Gold step, the gold adheres to the nickel-plated areas through molecular exchange and covers the nickel, protecting it until soldering, and control of the gold thickness within specified tolerances ensures the continued solderability of the nickel.Both ENIG and ENEPIG have their pros and cons. On its part, ENIG has potential advantages from the fact that it has a flat surface to its fast application and high-temperature resistance. On the other side, ENEPIG brags of strength in withstanding reflow cycles and truly reliable wire bonding. Depending on the application imperatives, each finish has its chastened uses. ENIG is mainly geared toward lead-free soldering, SMT, and BGA packages. Oppositely, ENEPIG is applicable for rigorous processes like THT, SMT, BGA, wire bonding, and press-fit technologies.<h3>ImAg (Immersion Silver)</h3>ImAg consists of a thin layer of immersion silver plating over copper traces. The standard procedure for making ImAg is as follows:<img src="https://img.pcbx.com/dev/file/image/article/20240807/3b3e503018c740b8896500c4053bb0b9.png" alt="ImAg Process-PCBX" data-href="" style="width: 100%;"/> <table style="width: auto;"><tbody><tr><td colspan="1" rowspan="1" width="auto" style="text-align: center;">Pros of ImAg Surface Finish</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">Cons of ImAg Surface Finish</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Planar surface; • Short, easy process cycle; • Inexpensive; • High conductivity; • Good for fine pitch product; • Copper/Tin solder joint; • Reworkable; • Not affect hole size ;</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Tarnish ; • Silver migration; • Planar micro voids; • Creep corrosion; ImAg offers a superior surface polish for soldering and testing. However, the main disadvantage is that it is prone to creep corrosion.</td></tr></tbody></table><h3>ImSn—Immersion Tin</h3>ImSn uses tin instead of silver, and one of the main advantages of this process is the very planar finish that it provides to the copper pads, which in turn makes it highly suitable for SMT applications. Another fast became the fact that ImSn offers a surface easily detectable by common <a href="https://www.pcbx.com/product/automated-optical-inspection" target="_blank">AOI</a> techniques used.<h3>OSP: Organic Solderability Preservatives</h3><a href="https://www.pcbx.com/article/general-knowledge-of-pcb-osp-surface-finish" target="_blank">OSP</a> belongs to the surface finishes using transparent organic material. The water-based organic compound can attach itself selectively onto copper, thus protecting it until soldering. The process of a typical OSP is as follows:<img src="https://img.pcbx.com/dev/file/image/article/20240807/1348b51938374546b4d879daff79873a.png" alt="OSP Process-PCBX" data-href="" style="width: 100%;"/> <table style="width: auto;"><tbody><tr><td colspan="1" rowspan="1" width="291.51" style="text-align: center;">Pros of OSP Surface Finish</td><td colspan="1" rowspan="1" width="297.34" style="text-align: center;">Cons of OSP Surface Finish</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Flat/planar; • Short, easy process cycle ; • Inexpensive; • Reworkable ; • Not affect finished hole size; • Copper/Tin solder joint;</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">• Multiple reflows ; • Limited shelf life ; • Not conductive ; • Difficult to inspect; • Limited thermal cycles ;</td></tr></tbody></table><h3>Summary</h3>Each type of surface finish has different advantages and disadvantages. Selection should consider end-use application, performance requirements, cost, corrosion resistance, ICT capabilities, hole fill, and other applicable parameters. The more variables used to compare, the more accurate your selection will be.Comparing Surface Finishes<ul><li style="text-align: left;">Cost: ImAg and OSP are the least expensive, with ENIG as the highest cost option.</li><li style="text-align: left;">Corrosion Resistance: HASL and ImSn are at the top; ImAg is last on the list.</li><li style="text-align: left;">ICT Capability: Essentially, all finishes are good, except OSP.</li><li style="text-align: left;">Hole Fill: HASL and ENIG are excellent compared to other finishes.</li></ul><h2>Surface Finish Selection</h2>Choosing an appropriate surface finish in the fabrication of printed circuit boards is very important for high process yields, low numbers of rework, low field failure rates, effective test capabilities, low scrap rates, and a lower cost. All significant factors related to assembly should be taken into consideration to ensure the final products are of a quality standard and performed accordingly.Each occupant has different selection criteria. More often than not, the chosen surface finish meets particular requirements and convenience at the cost of quality, performance, and reliability of the PCB.In light of the above descriptions of each type of surface finish, some attributes become very critical selection criteria. As one can tell from the form shown below, each of the types of surface finishes either has it or otherwise, giving a guideline for selecting the best option for the surface finish, considering the requirements and characteristics of your PCB products.<table style="width: auto;"><tbody><tr><td colspan="1" rowspan="1" width="auto" style="text-align: center;">Items</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">HASL</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">ENIG</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">ENEPIG</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">ImAg</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">ImSn</td><td colspan="1" rowspan="1" width="auto" style="text-align: center;">OSP</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Cost sensitive product</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">High volume required</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Cosmetics of surface finish</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Lead-free wave solder</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Fine pitch components used</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Requirement of wire bonding to surface finish</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">High yield ICT</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Lead-free shock/drop</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td></tr><tr><td colspan="1" rowspan="1" width="auto" style="text-align: left;">Possibilities of corrosion failure</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">x</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√</td><td colspan="1" rowspan="1" width="auto" style="text-align: left;">√ </td></tr></tbody></table>The ultimate in surface-finish selection should be to provide the optimal balance of the many functions. Each surface finish has its own list of pros and cons. Fortunately, there are techniques in engineering to help offset the negatives. Some examples are, to overcome the reduced wetting force of OSP, consider one or more of the following: improve the board solderability plating, alter wave solder alloys, or increase top-side preheat. It is all about taking every possible consideration to reach an optimum performance.The growing importance of environmental issues in the electronics industry has prompted different regulations recently, including <a href="https://www.pcbx.com/product/rohs-lead-free" target="_blank">RoHS</a>, or the Restriction of Hazardous Substances and Lead-Free, gaining its first appearance within the European Union through Directive 2002/95/EC. This directive bans the use of six hazardous chemicals in electrical and electronic equipment, and beginning July 1, 2006, all eligible products supplied in the EU market must be RoHS-compliant. RoHS compliance has a broad impact on the electronics industry, driving demand for lead-free surface treatments.&lt;button class="center btn-lg" data-href="/order/manufacturing/pcb"&gt;Check Prices with Different Surface FInish&lt;/button&gt;PCBX provides a convenient and free online price calculator to help you estimate the cost of PCBs with any of the following surface finishes. Click the button below to access the PCB quote page and see how prices vary with different surface finish options.

Selecting the right PCB surface finish, from options like HASL, ENIG, ENEPIG, and OSP, is crucial for preventing oxidation, ensuring solderability, and meeting reliability standards.

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