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Have you ever wondered why some circuits, like the RAM in a computer, have one side made from gold pins? What is the connection type, and what is the purpose and benefit of using this connection type? These are known as gold fingers, and here you will learn everything regarding what gold fingers are on PCB and their importance.
Gold fingers are gold-plated columns of connection points at one or many edges of a PCB. These are mainly used where two PCBs are required to be joined temporarily and quickly but also reliably with no issues in the performance. Computer graphics cards are a great example here, as a GPU is a whole PCB, and the computer's motherboard is a PCB.
The motherboard comes with the jack, while GPUs have gold fingers. With these, we can easily connect them with reliable performance, and this connection is not permanent, so that the GPUs can be pulled out easily. There are hundreds of other examples of gold fingers connecting two PCBs.
Saying that gold fingers have revolutionized the PCB industry won't be wrong. It is one of the most important yet underrated features of a PCB, and most components of a computer have already switched that previously came with the wired connections. Some examples of devices with gold fingers include:
Below are a few reasons why gold fingers are extremely important today.
Gold fingers make sharing peripherals very easy. One can simply pull a GPU from their PC and use it on any other supporting device.
With Gold fingers, you only have to replace the bad component. For instance, if one RAM stick is malfunctioning, you can pull it out and replace it with a new one. So, repairs and replacements will cost way less.
The longevity and compatibility become better. If an SSD is supported in one PC, it might also be supported in several other computers as long as the same female slot comes in the newer generations. So, you can use one peripheral for a long time.
Gold fingers create a plug-and-play experience where you don't need to work with soldering or wired connections. It makes upgrades significantly easier.
Gold fingers are designed according to their required applications. For instance, the M.2 SSD has its jack type where all M.2 supported devices can be connected. Similarly, all the RAM generations use different types of slots, so the gold finger design is different. Several examples are available from the computer world, which can be categorized into 3 main categories as follows.
With gold fingers, we can use special adapters, especially in cases where those special connections need to be made frequently. Using a wired connection for cards like GPUs and sound cards is not the right solution because of their bigger size. The gold fingers with these special adapters provide connection and support the card weight even when the card is attached and detached.
One of the most common uses of the gold fingers on a PCB is to allow external connections with the motherboard. The attachments with gold fingers are attached to the PC's motherboard, and they provide I/O ports outside the computer casing. Depending on the card attached, you can use several external devices like a Wi-Fi antenna, USB interface, etc.
Female slots like the ISA, PCI, or AGP slots let a secondary connected to the main motherboard. This connection uses gold fingers to transfer signals across the motherboard and the peripherals installed.
For some applications, the gold fingers provide power through the motherboard. However, other ones use external connectors for supplying power, and those connectors are connected to the power supply wires.
Gold fingers on PCBs were started manufacturing around 2 decades ago, and IPC established the production standards in 2002. These standards were changed several times, and according to the current standards, the following specifications must be met whenever gold fingers are used on a PCB.
Rigidity is essential for gold fingers, and they must be long-lasting as well. So, adding around 5 to 10% cobalt to the gold plating is essential.
Thickness is an important specification and must fall between 2 and 50 microinches. There are 4 standard thickness options used today which are:
Thicker gold fingers are good for PCBs that need regular plugging and unplugging because they must withstand wear and tear for a long time. On the other hand, thinner ones are used for prototypes generally for testing purposes.
Visual testing of gold fingers is essential to ensure that these are made of top quality with a refined surface. It is done with a magnifying glass, and the surface is checked for cleanliness, smoothness, and the right amount of gold plating with no appearance of nickel underneath.
The last standard is a tape test that checks the adhesiveness of gold against the PCB. The gold must be strongly stuck with the PCB, so even if it is inserted at a slightly wrong angle, it must not come off the PCB and stay there. To conduct this test, the tape is placed on the strip of gold fingers and removed to see if any finger platings have come off.
These are the 4 most common standards to meet when designing gold fingers on PCB, while several others include IPC updates.
Just like the PCB design and manufacturing process, the gold fingers on PCBs are also made with a thorough process. But before you begin with the process, it is essential to consider that the plated through holes on the PCB must never be near the gold fingers. Secondly, keeping the gold fingers facing opposite from the middle of your PCB is better, especially if you plan to bevel the edge of your PCB.
Additionally, there must be no contact of gold fingers with any solder mask or PCB screen printing. Keeping these away from the gold fingers results in a much better PCB design with higher reliability than gold fingers. If any of these design practices are not followed, the gold fingers may become incapable of communicating correctly with the PCB due to a bad fitting or connection.
Gold fingers are usually done on the PCB after it is manufactured. In most cases, these are done before attaching the components to the PCB, so it is important to cover the PCB except for the parts where the gold fingers need to be installed. This prevents the rest of the PCB and, most importantly, the solder points safe from anything during the plating process.
Next, sulfuric acid is used to wash away the oxidation layer on the surface of the PCB. It is don't to uncover the copper pads underneath; once this layer is removed, water is used to clean the copper surfaces. The grinding process is don't a little further to clean the PCB surface, and once all the unwanted layers are removed, deionized water and simple water are used to clean everything up.
Now the copper pads on PCB are electroplated with nickel. After the padding is complete deionized water is again used to clean everything of any unwanted particles. After cleaning, it is ensured that the pads are ready for gold plating.
Now gold is electroplated on the nickel-plated copper pads. After gold plating is completed, the PCB is again cleaned with deionized water. With that, the hard gold fingers are made with the help of nickel plating and gold plating on bare copper pads.
Glue removal is the next step which uncovers all the solder points of the PCB, making it ready once again to get solder and all the PCB components installed on it. As the components are installed, some PCBs are completed and ready to be used. However, before installing components and soldering them on the PCB, some PCBs go through the step of beveling, which is as follows.
Not all PCBs are beveled, but some are, and it helps easily install the gold fingers into their dedicated slots. Typically, the gold fingers are beveled at an angle between 30 and 45 degrees. After beveling, the PCB is finished and ready to be used as components are installed.
Gold fingers are the little golden connection pads we see on things like SSD, RAM, GPU, and other computer components. These are extremely important because they allow perpendicular connection allowing a solid and reliable yet temporary joint between two PCBs.