6 Layers Golden Finger PCB manufacturer

On the memory bars and graphics cards of the computer, we can see a row of golden-yellow conductive contacts called "golden fingers". PCB designs and manufactures Gold Finger, or Edge Connector, which uses the connector as an outlet to the external connection network. Next, we will learn how to handle the golden finger in PCB and some details.

Surface Treatment circuit board

1.Electroplated nickel and gold: The thickness can reach 3-50u.Because of its superior conductivity,antioxidant,and abrasion resistance,it is widely used on PCB which needs to be frequently inserted or PCB board which needs to be regularly mechanically abrasive. However,because of the high cost of gold plating,it is only applied to local gold plating.

2.Gold deposit: 1 u thick, up to 3 u thick" is widely used in high precision PCB board with key position, bonded IC, BGA design because of its superior conductivity, flatness and solderability. For PCB with low wear resistance requirements, the whole plate deposit process can also be selected. The cost of gold deposit process is much lower than that. The color of the gold precipitation process is golden.

Gold Finger Details Processing in PCB

1) In order to increase the wear resistance of golden fingers,it usually need to be electroplated with hard gold.

2) Chamfering required,usually 45 degrees,other angles such as 20 degrees,30 degrees,etc.If there is no chamfer in the design,there is a problem.The 45-degree chamfer in PCB is shown below:

3) It requires resistance welding and windowing of the entire piece, PIN does not require opening the stencil;

4) The minimum distance between the tin and silver solder pads is 14mil from the tip of the finger,it is recommended that the pad be more than 1mm from the finger position at design time,including through hole pads.

5) Do not lay copper on the surface of the golden finger;

6) All layers of the inner layer need to be cut with copper, which is usually 3 mm wide. Copper can be cut with half a finger or a whole finger.

Is it gold?

First,let's look at two concepts: soft hard gold. Soft gold, generally softer.Hard gold,allies a compound of hard gold.

The main function of the golden finger is to connect,so it must have good electrical conductivity,wear resistance,anti-oxidation,corrosion resistance.

Because pure gold (gold) is soft in texture,golden fingers usually do not use gold,but simply electroplate a layer of "hard gold (gold compounds)" on it,which can provide good electrical conductivity,wear resistance,and antioxidant performance of gold.

So has PCB ever used "soft gold"? The answer is certainly useful,such as the interface of some mobile phone keys, the aluminum wires on the COB (Chip On Board). Soft gold is usually electroplated to precipitate nickel and gold on the circuit board.Its thickness control is more flexible.

Why?

A unique PCBA needs to be interconnected to the motherboard but needs to be easily replaced, with golden finger and slot connections designed similar to the relationship between the power plug and socket

Gold is good in conductivity,inert and strong in inertia,which guarantees conductivity without oxidation,and good enough conductivity after frequent insertion.

How to select the technical requirements of the golden finger depending on the usage scenario.

Generally speaking, the golden finger means that these fingers are partially plated with 5-30u of hard gold,which has better wear resistance and guarantees 20,000 insertions without affecting the quality.It must be more than 5U thick.However,the process of hard gold processing is relatively complex,and the gold thickness requires more gold and salt to be consumed, which directly causes the cost to be too high.In fact,many PCBs do not need to be frequently plugged and unplugged.It is not necessary to make thicker gold, or even do not make hard gold, and do gold replacement directly (metalized in soft gold,generally 1-3U thick) to effectively reduce the purchase price of PCB.

Processing method 

Standard gold-plated fingers are electroplated, requiring all fingers to conduct electricity during electroplating, so wires are added underneath the gold finger by first plating a layer of dielectric nickel on the copper surface and then gold on the nickel layer at the required thickness.

Before the finger is gold plated, cover all other non-gold plated bonding pads with tape. After gold plating, tear off the tape and then cover the golden finger with tape. The other bonding pads are treated as required by spraying tin, OSP, gold and so on. Tear off the tape on the golden finger after the bonding pad is finished. The gold finger grinds the bevel during shaping for easy insertion into the slot.