1. PCB surface treatment:
OSP, HASL, Immersion gold, tin, silver, hard gold plated, gold plated, gold finger, nickel palladium OSP: cost lower, solderability is good, storage conditions are harsh, time is short, environmental protection technology, welding is good, smooth.
Emmersion Tin: the tin spray plate is generally a multi-layer (4-46 layer) high-precision PCB model, which has been used by many domestic large-scale communication, computer, medical equipment, aerospace enterprises and research units. The connecting finger is the connecting part between the memory module and the memory slot, and all signals are transmitted through the gold finger.
The gold finger is made up of many gold conductive contacts, so the gold finger is called "golden finger" because of its gold plated surface and the arrangement of conductive contacts.
Gold finger is actually coated with a special layer of gold on the copper clad laminate, because gold has strong oxidation resistance and strong conductivity.
However, due to the high price of gold, more memory is replaced by tinning. Since the 1990s, tinning materials have been widely used. At present, the "gold fingers" of mainboard, memory and video card are almost made of tin. Only the contact points of some high-performance server / workstation accessories will continue to adopt the method of gold plating, which is not cheap.
2. What is the use of gold plated boards?
With the increasing integration of IC, the more IC the more dense. The vertical tin spray process is difficult to flatten the pads, which brings difficulty to the SMT mounting, and the shelf life of the tin plate is very short.
The gilding plate solves these problems.
1, for the surface mount technology, especially for 0603 and 0402 super miniature sheets, because the flatness of the solder is directly related to the quality of solder paste printing process, and has a decisive impact on the quality of the reflow soldering. Therefore, the whole plate gilding is often seen in high density and small scale surface mount process.
2, during the trial stage, the influence of component procurement and other factors is not that the boards will be immediately welded. Instead, they will have to wait for weeks or even months. The life expectancy of shelf life is much longer than that of Pb Sn alloys.
Besides, not much difference between the cost of gold plated PCB and the tin lead alloy plate is observed.
But as wiring becomes more and more denser, the width and spacing have reached 3-4MIL.
Therefore, the problem of gold wire shorting is brought about. As the frequency of signal increases, the effect of skin effect on signal quality is more obvious.
The skin effect is the high frequency alternating current, and the current tends to concentrate on the surface of the wire. According to the calculation, the skin depth is related to the frequency.
In order to solve the above problems, the PCB of the gold plate has the following characteristics:
1, because the crystal structure of gold deposit and gold plating is different, the gold deposit will be golden yellow and more yellow than gold plated, and the customers will be more satisfied.
2, Shen Jin is easier to weld than gold plating, which will not cause bad welding and cause customer complaints.
3, because the gold plate only has nickel gold on the pad, the signal transmission in the skin effect effect will not affect the signal in the copper layer.
4, because gold deposition is more compact than gold plating, it is not easy to produce oxidation.
5, because the gold plate only has nickel gold on the pad, it will not produce gold wire and make it short.
6, because the gold plate only has nickel gold on the pad, so the resistance welding on the line is more firmly combined with the copper layer.
7, the project will not affect the spacing when making compensation.
8, because the crystal structure of gold deposit and gold plating is different, the stress of the gold plate is easier to control, which is more advantageous to the processing of the fixed products. At the same time, it is also because the gold sink is more soft than the gold plated, so the sunk board makes the gold finger not wearable.
9. The flatness and life expectancy of the sunken plate are as good as that of the gilding plate.
For the gilding process, the effect of tin is greatly reduced, while the effect of gold on the tin is better. Unless the manufacturer asks for binding, most manufacturers will choose to deposit gold under the usual conditions of PCB surface treatment.
Gold plating (gold plated, gold plated), silver plated, OSP, tin sprayed (lead and lead free).
These are mainly for FR-4 or CEM-3 and other plates, the paper base material and the surface treatment of rosin; the poor tin (poor tin), if we exclude the solder paste and other manufacturers and production process of materials.
There are only several reasons for this PCB problem:
1. In PCB manufacturing, is there an oil permeable film on the PAN position? It can block the effect of tin, which can be verified by the tin drift test.
2, whether the PAN position meets the design requirements, that is, whether the pad design can guarantee the supporting function of parts sufficiently.
3, whether the pad is polluted, which can be obtained by ion pollution test. The above three points are basically the key points of consideration for PCB manufacturers.
The advantages and disadvantages of several ways of surface treatment are their respective strengths and weaknesses.
Gold plating, it can make PCB store longer, and the outside environment temperature and humidity change is smaller (compared with other surface treatment), generally can keep a year or so; tin spray surface treatment secondly, OSP again, the two surface treatment in the ambient temperature.