High-Quality Gold Finger PCBs with Competitive Pricing

  • Norml, Subsection& Different Length Gold Finger
  • Gold Plating upto to 5um
  • Immersion Gold, Solf Gold & Hard Gold
  • Single-layer, Double-layer & Multilayer
  • ISO9001:2015 Certified & UL Listed
  • 100% E-testing, AOI Inspection & Visual Inspection

A Brief Introduction to Gold Finger PCB

Gold finger PCB is a printed circuit board with gold-plated connectors at one side or several sides. On such kinds of PCBs, there are copper pads on top and (or) bottom side. The pads are free from solder mask and they are plated by 10 to 100 micro inches thickness hard gold. As these pads are designed with equal size and same direction, and they look like fingers, they are called gold fingers.

Gold fingers PCBs are usually used as quick plug-in and out devices, such as USB flash drives and DDR4 RAM, these products need to be plugged in and out many times. As gold resists oxidation and also has very high conductivity, gold fingers are the best choice for such kinds of PCBs. So gold finger PCBs play a very important role in the electronic industry.

Since a relatively thick layer of gold will be needed on gold finger PCBs, it is obvious that the cost of gold finger PCBs is higher than standard circuit boards with immersion gold (ENIG).

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    Classification and Identification Features of Gold finger

    Gold finger is one of the surface technology for PCB. It can be divided into an ordinary gold finger ( flat finger ), subsection gold finger ( discontinuous gold finger ), different length gold finger (crooked gold finger ), PCB fingers details as below:

     

    1. Ordinary gold finger

    Arranged neatly on the edge of the PCB, the length and width are the same as the rectangular pad.

    3. Different length gold finger

    Rectangular pads located at the edge of the PCB, but with different lengths.

    Maybe you have the question, “Why does the PCB need to make gold fingers of different lengths?” Take a glimpse at the following reasons.

    2. Subsection gold finger

    Rectangular pad, the positions of their lengths on the PCB edges are different, and the front section has been disconnected.

    Surface Treatment of Gold finger PCB

    It is known that the copper in the PCB material is mainly red copper, and the copper solder pads exposed to the air are easily oxidized. What can be done to prevent this from happening? Surface treatment of the PCB’s copper solder pads is very effective.

    Gold fingers are a surface treatment technology of PCB. Still, if the whole PCB surface plating hard gold will be costly, we usually use combined surface treatment to save costs. Let’s explain in detail below.

    1. What is Immersion gold treatment?

    Immersion gold treatment is a type of metal finishing process used in the electronics industry to protect and enhance the surface of metal components. We usually use ENIG to represent it. This process involves dipping the component in an immersion gold solution, which deposits a thin layer of gold onto the component’s surface. This thin layer provides excellent corrosion resistance, electrical insulation, and wear resistance.

    Furthermore, immersion gold treatment is a cost-effective and efficient way to protect metal components from environmental damage.

    The immersion gold treatment process involves a series of steps, including cleaning, activation, plating/immersion, rinsing, passivation, and drying.

    2. What is hot air leveling ( HAL )?

    PCB HAL, also called hot air leveling, is an essential surface treatment technology of PCB. HAL mainly have Lead free HAL and lead HAL, two technology types. It is also commonly used and widely used by PCB manufacturers. The process can be divided into Pretreatment ( remove oil, get clean and fresh pads ), preheat ( can shorten tin dipping time, reduce thermal shock, reduce the temperature drop of the tin furnace), scaling powder ( clean copper surface, reduce the cohesion of Sn Pb, make the welding pad flat ), hot air leveling, post-treatment ( Waste tin washing, DI water washing, drying ).

    The advantages of HAL technology are the practical process, good welding performance, good oxidation resistance, affordable price and high-cost performance.

    3. How to combine surface treatment with gold finger PCB to save cost?

    The cost of immersion gold technology is higher than other production hot air leveling (HAL ) technology. For example, the gold thickness requirement is over the standard technology. In that case, the cost is higher, so if you need the standard requirements for the weldability and electrical properties of PCB, you can choose a more economical surface treatment like hot air leveling ( HAL ) or lead-free hot air leveling ( LFHAL ).

    But if you have high requirements for your PCB’s solderability and electrical properties, you must choose immersion gold technology. For: if your PCB have a gold finger in PCB need to make with immersion gold finishing, or the trace width/gap of the pad is not enough, it is better to make immersion gold + plating gold finger technology to make it. That will make the PCB have excellent weldability and very stable electrical properties. So the pad will not fall off easily, not have poor contact and will short phenomenon. And also shockproof and fall prevention. So, of course, we won’t fall off the board.

    Another method to save cost if the PCB have gold fingers is that except for the finger part, the rest parts of the surface can choose HAL technology according to some situation, that is, HAL + plating gold finger technology, the conditions are enough to the trace width and gap of the pad, and the not very high welding requirements, use HAL + plating gold finger technology can lower the production cost-effectively, and not affect the use of PCBs at the same time.

    But if more than the trace width and gap of the pad of the PCB is needed, then using HAL technology will increase the production difficulty and may cause a tin bridge etc., and also may cause poor contact phenomenon when the finger is frequently insertion and stripping.

    So, according to your PCB’s actual situation, you can choose to elect a suitable PCB surface treatment-making process, and then you can control the cost without affecting the use of boards.

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    The Main Two Technologies Commonly Used for Gold Finger Plating at Present

    1. One technology is the lead wire from the gold finger terminal as the gold plating wire.

    After finishing the gold plating, remove the wire using the milling profile and etching method. But, the products made by this technology will have lead wire residue around the gold finger in PCB, which will cause copper exposure to be unable to meet the requirement that copper exposure is not allowed.

    2. The other technology is not lead wire from the gold finger.

    Still, lead wire from PCB inner layer or outer layer circuit that connects with a gold finger then achieves gold finger plating, so avoid copper exposure around the gold finger. But when the circuit density is very high, the circuit is minimal and dense inside PCB. So using this technology will not make the lead wire in the circuit Layer; this technology is powerless to isolate the gold finger ( the gold finger does not connect to any circuit ).

    The advantages and disadvantages of plating gold finger

    After finishing the gold plating, remove the wire using the milling profile and etching method. But, the products made by this technology will have lead wire residue around the gold finger in PCB, which will cause copper exposure to be unable to meet the requirement that copper exposure is not allowed.

    Advantages

    The thickness can reach 3-50u “, with high hardness, wear resistance and resistance to oxidation.

    Disadvantages

    Plating gold will easily cause the gold wire to be short, the solder strength is poor, the cost is higher, skin effect could be more conducive to high-frequency signal transmission.

    Common Problems and Treatment of Plating Gold Fingers

    Cause: The concentration of gold needs to be increased; Proportion needs to be higher; Insufficient stir; nickel copper pollutes gold plating liquids.

    Solutions: Add gold salt; Increase the proportion; Strengthen the stir; Clean the metal pollution.

    Cause: Poor adhesion between copper and nickel; Poor adhesion between nickel and gold; Poor cleaning treatment before nickel and gold plating; High stress of nickel plating layer.

    Solutions: Pay attention to the effect of copper treatment before nickel plating; Pay attention to the impact of nickel treatment before gold plating; Strengthen the treatment effect before plating; Purify plating liquid. Carry out towing or carbon treatment for nickel cylinders.

    Cause: Too few additives; High PH value; Plating liquid was polluted by metal ions.

    Solutions: Replenish moderate additives; Adjust the PH value; Remove the metal ions pollution. Pay attention to prevent pollution at ordinary times, especially the frequent Nickle ions pollution.

    Cause: Clean and dry, not thorough; plating card edge connector PCB stock in a corrosive environment.

    Solutions: Enhance cleaning and drying effect after gold plating; Plating gold PCB should stock far away from the corrosive environment.

    Cause: The gold finger is exposed and touched with the air for a long time, and the surface of the gold finger will form an oxidation layer. Also, there will have dust adhesion causing the resistivity of the contact surface is increased, resulting in poor contact.

    Solutions:
    1. Using an ordinary eraser on the market can remove the oxidation layer and dust.

    2. Use a pencil to remove the oxidation layer. The ingredients of the pencil are graphite and clay, clay has a certain hardness that can remove the oxide layer, and graphite are electric conductor, so if there is graphite residue after wiping the gold finger, it may cause a short circuit of adjacent contacts, therefor, after wiping the gold finger, should check if there is any graphite residue in the crevice. If there is, please be sure to clean it up.

    3. Use PCB washing water. Use the cotton swab, cotton ball or dust-free cloth to dip in the washing water to wipe the golden finger. After drying completely, you can use it. If you can’t get any PCB washing water, you also can use the organic solvent of Anhydrous ethanol or Anhydrous isopropyl alcohol to replace it. Please avoid inhaling too much steam during operation to prevent health hazards.

    Appearance Inspection Standard for Gold Finger PCB:

    In standard PCB manufacturing, hard gold plating PCB are made as “solder mask opening “, which means no soldered mask (green oil) between the pad of the gold finger to avoid solder mask drop off due to long-term plugging, and then affects the quality of the products. Besides, solder mask openings have another universal function. For example, the thickness of copper foil can be increased during tin ironing in the middle and late stages to avoid the excessive current common in power and motor control system boards.

     

    Convex angle

    A. When the gap between two gold fingers is greater than 0.38 mm ( 15mil ), it can accept a convex angle, but the space at least has two-thirds of the gap.

    B. When the gap between two gold fingers is less than 0.38 mm ( 15mil ), this board can’t accept the convex angle phenomenon.

    Break

    The break area in a single gold hand area shall not exceed 20%. If the break area is less than 20%, each side of the gold finger in PCB can’t be over two positions break ( including two positions ).

    Scratch

    A. The scratch part of the gold finger can not expose base material (copper or nickel).

    B. The scratch of a gold finger without exposed substrate shall not exceed 1/5 of the gold finger index on one side.

    A Few Design Rules and Notes for PCB Gold Finger:

    The Panel Mode for Gold Finger PCB

    1. Without side strips

    Some customers need to add side trips for four sides, including the gold finger part for the panel. That is also ok, but some manufacturers cannot make that. Here in Viasion, we can do that very well. 

    2. With side strips

    The standard panel mode for hard gold pcb is panel back to back to make the gold finger face outward. It will be convenient for production. Generally, this method does not add side strips in the gold finger position.

    The Function of Gold Finger Lead Wire

    How to Remove the Gold Finger Lead Wire?

    Remove the gold finger lead wire by beveling it for a neat gold finger.

     A secondary etching process is usually required when dealing with the lead wire of gold fingers of different lengths. Simply speaking, the first etching process is etching the circuit of PCB, then using dry film or a peelable blue mask to cover the circuit area to plating the gold to the gold finger area by gold finger lead wire next are cover all other areas but the gold finger lead wire by dry film, at last, secondary etching the gold finger lead wire.

    Interesting Knowledge of Gold Finger PCB

    Some people will ask, ” Is gold in gold fingers real gold? ” Firstly, let’s look at two concepts associated with the gold finger: Soft gold and hard gold. Soft gold refers to the soft gold texture, while hard gold refers to the gold texture made by a gold chemical compound.

    Using pure gold to make the gold finger with properties such as good electrical conductivity, wear resistance, and oxidation resistance is not appropriate to make the gold finger. Instead, we need to plate a layer of “hard gold” (gold compound) on top of the gold finger.

    Back to the question if gold in the gold finger is real gold, the answers are no matter plating soft gold or hard gold, the gold content is minimal, so don’t dismantle electronic instruments to “withdraw gold”.

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    Frequently Asked Questions

    PCB gold finger refers to the pads used for inserting into the slot and the pads similar to the finger arrangement for contacting and conducting with the metal spring in the slot.

    Ordinary gold finger
    Subsection gold finger
    Different length gold finger

    There are different repair methods for various problems. For example, to deal with the problem that there is tin on PCB gold fingers, the following techniques can be used.
    1) First, use the suction line to clean up the solder slag
    2) Then use alcohol or board washing water to wipe clean the dirt
    3) Then use liquid with gold to re-cover the gold finger.

    PCB gold fingers are typically made from a thin layer of gold plated onto a metal conductor. The thickness of the PCB gold finger is determined by its application and can range from 5 microns to 100 microns.

    PCB gold fingers have good electrical conductivity, wear resistance, oxidation and corrosion resistance.
    Gold fingers play the role of docking with another PCB with the exact specifications of the female chassis or being soldered together with the exact specifications of the pad to achieve some functional purposes.

    The design requirements of gold fingers are as follows.
    The thickness of gold on the gold finger is generally 0.25-1.3um, the thickness of gold according to the number of times the gold finger is inserted and removed.
    The minimum distance between gold fingers is six mils.
    Gold finger boards are designed for a thickness of 0.8-2.0mm.
    The maximum height of gold fingers is two 2inch.
    The chamfer angle of gold finger can be 20°, 30°, 45°, 60°, 90°.
    The minimum spacing from sink tin/silver pads to the top of the gold finger should be 14 mils.

    Gold fingers connected with slots make it easier to replace a PCB with a unique function that needs to be interconnected with the mainboard.

    Making standard hard gold-plated fingers requires an electroplating method and needs to conduct electricity when plating all gold fingers. Therefore, wires are added underneath the gold fingers. A layer of dielectric nickel is first plated on the copper surface, then gold is plated on top of the nickel layer at the required thickness.

    All other non-gold plated pads are covered with tape before performing gold plating on the finger. After gold plating, tear off the tape and wrap the gold finger with tape. Other pads spray tin, OSP, gold, etc., processing as required and tearing off the tape on the gold finger after the pad processing is complete.

    3) When forming the bevelled edge of the gold finger, inserting it into the card slot is convenient.

    The chemical composition of PCB gold fingers is Ni and Au.

    The standard thickness of PCB gold fingers is 30 to 50 micro inches. 

    The external PCB and motherboard can be interconnected through the contact conduction between the gold finger and the spring-loaded tab in the slot. At the same time, it is easy to disassemble and replace the PCB due to the difference in performance requirements of users.

    PCB gold fingers feature a tapered, bevelled edge to mate two PCBs and provide a secure connection between them quickly. This bevel is explicitly designed for PCB gold fingers to hold the mating PCBs together more securely and provide more reliable contact.

    PCB gold fingers are used to distribute power in PCBs (printed circuit boards) securely. PCB gold fingers are specially designed contacts that transfer energy and data signals between PCBs. PCB gold fingers are usually made from gold or a gold alloy, which provides conductivity and durability.

    For PCB boards that often need to be plugged and unplugged, the gold fingers usually need to be plated with hard gold to increase the wear resistance of the gold fingers.
    The gold finger must be chamfered at 45° at other angles such as 20°, 30°, etc. If there is no chamfering in the design, there is a problem.
    Do not lay copper on the surface of the gold finger.
    All layers of the gold finger’s inner layer need copper cutting. Usually, the width of copper cutting is greater than 3mm; you can do the half-finger copper cutting and whole-finger copper cutting.

    The gold finger on the PCB generally has a corresponding gold finger connector, such as the PCI slot in the computer motherboard.

    It is because gold is exceptionally resistant to oxidation and is highly conductive.

    There are two main types of gold finger-plating processes commonly used today.

    One is from the gold finger end leads. As a gold-plated wire, gold plating is completed by milling the shape or etching the way the lead is removed.

    Another is not from the gold finger lead but from a gold finger connected to the inner layer of the circuit board or the outer layer of the line lead, gold finger gold plating, to avoid copper exposure around the gold finger.

    The commonly acceptable IPC standard for gold fingers is IPC A-600 and IPC-6010.