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PCB Design

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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In this highly complex world of new-generation electronics, printed circuit boards (PCBs) have become the foundation. In computerized devices, mobile gadgets, and any kind of industrial machinery used in today's modern world, the transmission of digital signals is very important. Gold fingers are the crux of this connectivity; they are narrow, gold-plated connectors positioned along the edges of PCBs. This all-inclusive guide to PCB gold fingers gives all the details to understand gold fingers, their importance, types, the gold-plating process on them, and their diverse applications.<h2>What are Gold Fingers of Printed Circuit Boards?</h2>Gold fingers are the edge connectors in PCBs that are plated in gold. These are interface points into other boards or components for proper communication and flow of power. These fingers are normally made from hard gold, which is to say gold that has been electroplated, so as to take the pushing and shoving in and out without failure. The normal thickness for gold is from 2 to 50 microns. Which thickness should be used is dependent on what application it is being used for.We use gold for these connectors as it has the best corrosion resistance and is an excellent electrical conductor. It is relatively hard and durable and is often alloyed with nickel or cobalt for even greater hardness and durability, so the fingers are created to be extremely hardy and to survive for long periods under heavy use.<img src="https://img.pcbx.com/dev/file/image/article/20240912/89165b69b86d4a47a091d17a492961b1.jpg" alt="Gold Fingers-PCBX" data-href="" style="width: 100%;"/><h2>Type of Gold Fingers</h2>The ways of making the finger pads differ mainly in the gold plating thickness and the hardness:Electroplated Hard Gold: Suited for the most demanding of applications where contacts need to be mated over and over again, this process results in a deposit of approximately 30µ inches of hard gold that has excellent resistance against wear.Electroless Nickel Immersion Gold (ENIG): Although this process is far more economical than plating with hard gold and easier to solder, the yield golf is much softer and not recommended for most high-abrasion contacts. It's generally plated from 2 to 5µ inches.<h2>The Manufacturing Process: From Concept to Connection</h2>The Gold Fingers Plating process is voluminous and gives a constant high-quality product due to the following important steps: Nickel Plating: This is the first process in which a layer of nickel up to 2 to 6 microns deep is put over the connecting edges of fingers. This base layer acts as a substrate to improve adhesion and endurance of the gold layer, which follows.Gold Plating: A hard layer of gold (generally compounded with cobalt to make it harder) is elec­troplated over the nickel. The thickness is in the order 1 to 2 microns.Beveling: The edges of the fingers are bevelled at a specific angle (usually about 30 to 45 degrees) to enable free entry into their slotted count­erparts.<h2>Post-Plating Inspections and Tests</h2>Each PCB undergoes a series of testings and inspection to determine the quality of the gold plating:Visual Inspection: This is done using magnifying glasses where the smooth and clean contact edges have to be checked.Adhesion Test (Tape Test): This is done by attaching a strip of the tape to gold plated contact edges, then removing it hence gets inspected for the presence of the gold on the tape hence helps in determining sufficiency in the plating adhesion.<h2>Design and Specifications</h2>Gold finger design on PCBs shall strictly be within specific dimensions and per particular standards for proper performance:No PTH (plated through-holes) or pads shall be closer than 1mm from the gold fingersBetween the gold fingers and the PCB, there should be a space distance of 0.5mm.From the edges of the PCB, there shall be at least an exclusion of the inner copper layers so that they don't be exposed during beveling.The total length for gold fingers for plating has been taken to be of 40mm.<img src="https://img.pcbx.com/dev/file/image/article/20240912/617a78a16e914763a111b7ba715325e5.png" alt="Gold Fingers Design-PCBX" data-href="" style="width: 100%;"/><h2>Uses of Gold Fingers</h2><h2>Gold fingers are used in various other sectors. Some of its uses are given below:</h2>In-House Connections: The motherboard is connected to the main PCB with the help of secondary PCB, and such PCB has the gold fingers which slide into the female connections PCI, ISA or AGP.Special Interfaces: It is used in special booster peripheral equipment such as soundcard and graphics card.Peripherals: Gold fingers can be found at the edge of the motherboard. The use of gold fingers in the motherboard enables peripheral devices, such as the monitor, printer, USB devices, and even speakers, to be inserted into the motherboard slots, and allows these devices to be frequently plugged and unplugged.<h2>Types of Gold Fingers in Specialised PCBs</h2>Segmented or unequal of gold fingers can exist for special PCBs:Non-uniform Fingers: For example, in memory card readers, where shorter fingers have been designed so that some parts of the device can receive power supply before other parts.Segmented Fingers: These segmented connectors are used primarily in rough and waterproof electronics, that too, in very selective applications where a higher degree of rugged utilization is needed.<h2>Gold Finger Standards and Regulations</h2>Association Connecting Electronics Industries–IPC has taken initiatives to develop standards to ensure quality and reliability of PCB gold fingers :Chemical Composition: The gold plating that is characterized by maximum edge rigidity shall consist of 5 to 10% cobalt.The gold thickness needs to range from 2 to 50 microinches. Selected single requirements are 0.031 inches, 0.062 inches, 0.093 inches, and 0.125 inches.Tape and Visual Tests: This will ensure the plating can't be ripped off, plus it's uniform, and adheres well.<h2>The Collision of Technology and Formulation</h2>Currently, gold fingers are used in consumer and industrial machinery, from personal computing devices to manufacturing machinery. Robotic arms and other automated systems get their required power and signal from gold fingers. In consumer electronics, they ensure a smooth interface of so many devices, contributing to techno advancement.The gold fingers have become the indispensable making element of solid, reliable connections in wide ranges of application inside modern electronics. Due to their excellent conductivity and durability, as well as conformance with high standards, they are applicable in popular devices and complex industrial systems. With great production quality and rigid testing protocols, the manufacturer, Gold Fingers, goes a step further in assisting the big strive for innovations in many fields, which sets the golden standard in PCB technology.

Gold fingers are essential gold-plated edge connectors on PCBs, known for durability and conductivity, crucial for transmitting digital signals in electronics. They come in Electroplated Hard Gold and ENIG types. Used in motherboards, peripherals, and industrial machinery, they adhere to IPC standards ensuring reliable, high-quality connections in modern electronic devices.

The Essential Guide to PCB Gold Fingers

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.