Is it important to the surface of the PCB board of gold ?

A PCB board, surface treatment: antioxidant, spray tin, lead-free spray tin, gold, tin, immersion silver, gold plated, the entire board gold, gold finger, nipdau OSP: low cost, good solderability, storage conditions, time is short, environmental protection technology, welding, good leveling.


The surface of the PCB board of "gold" how important?


HASL: HASL general multilayer (4-46) high precision PCB model, have been several large-scale communications, computer, medical equipment and aerospace enterprises and research units can use finger is a connection between the memory and the memory slot, all signals are transmitted by Kim finger.


The gold finger is made up of a large number of golden conductive contacts. It is called gold finger because of its gold-plated surface and conductive contact sheets arranged in the shape of fingers". The gold finger is actually covered with a special layer of gold on the copper clad board, because gold has strong oxidation resistance and strong conductivity. But because the gold expensive, currently more memory are used instead of tin, from the last century began in 90s started to spread the tin materials, motherboard, memory and graphics and other equipment of the "golden finger" is almost always used tin materials, accessories contact only part of high performance server / workstation to the gold-plated approach, the price of natural cheap.


Two, why use gold-plated plates?


With the integration of IC higher and higher, the more IC feet, the more closely. The pad blowing flat and vertical tin spray process is difficult to be fine, which gives the SMT mount brought difficulty; in addition HASL inactive life is very short. The gold plate just solved these problems:


1, for surface mount technology, especially for the 0603 and 0402 ultra small surface mount pads, because the quality is directly related to the smooth process of solder paste printing, on the back of the reflow welding quality plays a decisive influence, therefore, the whole plate gold in high density and ultra small surface mount technology in common.

2, at the trial stage, affected by factors such as the component purchasing tend not to immediately board welding, but often have to wait a few weeks or even months before use, gold plate for life (shelf life) many times longer than Pewter so we are willing to adopt. Besides PCB in the stage of gold plating the cost and Pewter plate compared with not much difference between.

But as wiring becomes denser, the line width and spacing have reached 3-4MIL.

Therefore, the problem of gold wire short circuit: as the signal frequency is higher and higher, the influence of skin effect on the signal quality is more obvious when the signal is transmitted in the multi layer.

Skin effect is: high frequency alternating current, current will tend to focus on the surface of the wire flow. According to calculation, the depth of skin depends on the frequency.


Three, why use the golden board?


In order to solve the above problems of gold plated plate, the PCB with gold plate is mainly characterized by the following characteristics:

1, because sink gold and gold-plated formed by the crystal structure is different, Shen Jin will be golden yellow, more yellow than gold-plated, more satisfied with the customer.

2, because of the gold and gold-plated formed by the crystal structure is different, sink gold than gold-plated is easier to weld, will not cause welding bad, cause customer complaints.

3, because the gold plate only welding pad has nickel gold, skin effect in the signal transmission is in the copper layer will not affect the signal.

4, because the deposit is more gold-plated, the crystal structure is more dense, not easy to produce oxidation.

5, because the gold plate only welding pad has nickel gold, so it won't produce gold wire, cause short.

6 because the gold plate only has nickel gold on the pad, so the bonding of the welding on the line and the copper layer are more solid.

7, the project will not affect the spacing when making compensation.

8, because the deposition of gold and gold-plated crystal structure is different, the stress of its gold plate is more easy to control, for the products of the state, it is more conducive to the processing of bonding. At the same time, because the gold is more soft than the gold plating, the golden board is not wearable.

9. The flatness and the service life of the gold plate are as good as that of the gold plated plate.


Four, sink gold plate, VS gold-plated plate


In fact, the gold-plated process is divided into two kinds: one is electroplated gold, the other is sunken gold.


For the gold plating process, the effect of tin greatly, and heavy gold tin effect is a little better; unless required by the manufacturer is bound, or now the majority of manufacturers will choose gold craft! The common case of PCB surface treatment as follows: gold (gold plating, gold OSP), silver plated, spray tin (lead and lead free), which are mainly aimed at FR-4 or CEM-3, the paper sheet, base material and coating rosin surface treatment; tin (tin side) the bad if you exclude the reason etc. patch manufacturers in terms of technology and material.


Gold, it can make the PCB a long storage period, but also by the change of environmental temperature and humidity outside the small, generally can be stored for about a year; tin spraying surface treatment by OSP again, the two kinds of surface treatment in the environmental temperature and humidity storage time should pay attention to many.


 

(Source: internal information)

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