In the modern interconnected world of computers and wearables, signals are transmitted between different devices more than ever. For commands to be executed, communication must happen between two or more PCBs. And this is impossible without the use of gold fingers, which act as linking contacts between motherboards and other electronic parts such as graphics and sound cards.
This article presents a detailed guide on what gold fingers are, the design specifications for PCB gold fingers, their uses and limitations, and the regulations, guidelines and standards surrounding gold fingers.
What are PCB Gold Fingers?
Gold fingers are basically the gold-plated connectors found along PCB edges. As mentioned in the introduction, gold fingers are primarily used to link motherboards with other secondary circuits. Apart from computers, PCB gold fingers are found in other devices that heavily rely on digital signal communication, like smartphones and wearables.
Gold fingers are made of flash gold – one of the hardest golds in existence. The manufacturing specifications of gold fingers should be accurate, with their thickness ranging from 3 Us-50 Us.
Why are PCB Fingers Plaited with Gold?
Generally, circuit board contact points are exposed to regular insertion and ejection because of their interconnection role. Therefore, without a stable contact edge, the fingers will quickly wear out and hinder the device’s performance. The process of plaiting these contact parts with gold improves their durability.
But someone can ask: why do manufacturers prefer gold to other metals in plaiting these edge connectors? Isn’t gold a rare and expensive mineral? Isn’t copper a good conductor and a cheaper alternative? Well, though gold plating is costly, it is a necessity in this case.
Gold is preferred to other minerals because it has excellent corrosion resistance, super electrical conductivity after copper, and can be alloyed with cobalt or nickel to improve its resistance to wear and tear.
Besides, gold is inert – it rarely reacts with other metals. The feature makes gold suitable for making contact parts, which are more exposed to wear and tear and likely oxidize. While silver is sometimes used, it is not ideal for commercial use since it easily reacts with sulfides and chlorides.
How to Make PCB Gold Fingers
The primary step in making gold fingers is the gold plating process. You need a circuit board, a plating bar and follow the laying specifications. During PCB manufacturing, gold is applied after soldering. Mostly, manufacturers carry out surface finishing before gold plating their boards. The gold plating process discussed below assumes that you have a circuit board, and you are just remaining with gold plating its edges to make it more durable.
The Gold Plating Process
- First, you should plate between 3-6 nickel microns to the connector fingers.
- Secondly, add 1-2 gold micron layers to the connector fingers.
- Thirdly, bevel the layers accurately to facilitate attachment of the PCB to its slot.
Due to Gerber files and circuit designing advancements, gold fingers have progressed into advanced designs to meet various production needs. Unequally sized edge connectors (USEC) and segmented gold fingers (SGF) are famous circuit board gold fingers.
Some applications require shorter and longer fingers in the same board, such as memory card-reader boards. The purpose of shortening some fingers is to power the devices connected with the long fingers before those linked to the shorter fingers.
An image of a traditional memory card reader, source
SGFs are used to link circuit boards of hybrid devices. They contain fingers of various lengths and segments. SGFs are commonly applied in water-resistant and rugged equipment.
Segmented gold fingers, source
Limitations of the Gold Fingers PCB Technology
While the gold finger technology is a revolutionary technique, it has not found wide application because:
- Plated pads are located on the PCB edges. Since gold plating requires electroplating, the plated pads must be linked with the panel frame.
- Most plating pads cannot make gold fingers that stretch over 40nm. Therefore, if you want longer fingers, you may incur high manufacturing costs.
- The internal edge connector layers should not contain any copper material to prevent the beveling process from exposing the substrate.
- Apart from flex circuit boards, when plating the top and bottom PCB sides, the minimum allowable space between them should be 150nm.
Design Specifications for PCB Gold Fingers
Like other electronic components, circuit board gold fingers also have their specific designs and specifications. This section will address the design specifications for circuit board gold fingers. If you are planning to make a complete PCB, these points will be helpful to you.
Ensure the internal PCB layers do not contain copper. Copper creates too much contact during beveling when it’s found in the inner layers. Extra connection during beveling is unnecessary; thus, avoid using copper substrates in the internal PCB layers.
PCB with plated-through holes (PTH) should be postulated carefully. Position the PTHs in a 1mm region of the gold fingers. In other words, ensure a 1mm distance between the gold fingers and the holes.
Do not associate the PCB outline with the gold fingers. Instead, space them 0.5mm away from each other. These spacing measurements are standard, and any adjustment might cause malfunctioning.
The PCB surfaces are full of solder masks and screen printings. However, you must ensure that these solder masks and screen prints contact the gold fingers.
While designing your board, ensure that the gold fingers are not facing the middle part of the board.
Applications of Gold Finger PCBs
Gold fingers connect a circuit board to a source of power – one of the major applications of contact edges is linking a module circuit board to a source of power on the linking profile of a giant board.
They facilitate the transmission of signals – categorically, gold fingers connect with other circuit boards to facilitate signal transmission between the peripheral and central PCB.
Thirdly, gold finger interconnects modules in one PCB – traditional electronic devices consist of multiple stable modules that cannot be interconnected easily in the same PCB. The invention of flex PCBs facilitated the interconnection of several modules within one PCB.
They create space for future improvements. Think about a motherboard lacking ports and expansion slots? How does that even sound? How can it function, and how can designers improve it without introducing expansion slots? It is impossible. You cannot link the input and output devices. Designers cannot enhance their keyboard or mouse. Generally, without gold finger circuit boards, electronic devices cannot be improved.
Gold finger PCBs offer connections for data transmission on network-enabled gadgets such as network sim cards and other networking circuit board modules.
They link domain adapters. Edge contacts offer an attachment place for special adapters such as flash disks. These unique modules boot out some processing roles from the primary PCB during computation.
They link other gadgets to the primary processing PCB. In addition to the benefit of linking network modules and special adapters, gold fingers link peripheral electronics to the primary PCB.
How are Gold Finger PCBs Changing the World?
As highlighted above, the interactions between the main PCB and the intermediary PCBs are necessary for flawless connectivity. Apart from the rapid technological developments, smartphones, personal computers and other electronics are trending towards faster and more advanced features. As technology becomes more innovative, the applications and use of PCB gold fingers also increase. Thus, Gold-plated PCBs are the main drivers of the technological smartness we see today.
The gold contact edges facilitate the insertion and ejection of accessory devices and intermediary PCBs. Most consumer electronics and the internet of things rely heavily on gold fingers to function. The advancement of PCB gold fingers and the continuous improvement in their performances will significantly influence the development of smart tech.
Creating PCB gold fingers that follow the international manufacturing standards is not a walk in the park, especially for small-scale producers. Accuracy is an important factor, and quick turnaround times are also essential. Have you been wondering how you will maneuver through the manufacturing process of PCB gold fingers?
Worry no more! If you want your PCB gold fingers manufactured to precision at competitive market prices and quick turnaround times, kindly send us an online quote now. As the leading PCB manufacturer based in Shenzhen, China, we strive to produce the highest quality PCBs that meet the client’s requirements.