1. PCB Board Surface Treatment
Hard gold plating, full plate gold plating, gold finger, nickel palladium gold OSP: Lower cost, good weldability, harsh storage conditions, short time, environmental protection process, good welding, smooth.
Tin spray: The tin plate is generally a multi-layer (4-46 layers) high-precision PCB template, has been a number of large communications, computer, medical equipment and aerospace enterprises and research units can be used (gold finger) as the connection between the memory and the memory slot, all signals are transmitted through the gold finger.
Goldfinger is made up of a number of electrically conductive contacts that are gold in color and are arranged like fingers, so it is called "Goldfinger". Goldfinger is actually coated with copper by a special process because gold is highly resistant to oxidation and conduction.
However, because of the expensive price of gold, more memory is used to replace tin, from the 1990s began to popularize tin material, the current motherboard, memory and graphics card and other equipment "Gold finger" Almost all use tin material, only part of the high-performance server/workstation accessories contact point will continue to use gold plating, the price is naturally expensive.
2. The Reason For Choosing The Gilt Plating
As the integration of IC becomes higher and higher, the IC feet are denser and denser. The vertical tin-spraying process is difficult to flatten the thin pad, which brings difficulties to SMT mounting. In addition, the shelf life of the tin spray plate is very short. And the gold-plated plate solves these problems:
(1) For the surface mounting process, especially for 0603 and 0402 ultra-small table paste, because the flatness of the welding pad is directly related to the quality of the solder paste printing process, and plays a decisive influence on the quality of the reflow welding behind, so the whole plate gold plating in high density and ultra-small table paste process often see.
(2) In the trial production stage, affected by components procurement and other factors are often not the board to immediately weld, but often have to wait for a few weeks or even months to use, the shelf life of the gold plate is many times longer than the lead-tin alloy, so we are willing to use. Moreover, the cost of gold-plated PCB at the sampling stage is almost the same as that of a lead-tin alloy plate.
But with more and more dense wiring, line width, and spacing has reached 3-4mil.
Therefore, it brings about the problem of the short circuit of gold wire: As the frequency of the signal becomes higher and higher, the signal transmission in the multi-coating caused by the skin effect has a more obvious influence on the quality of the signal.
Skin effect refers to high-frequency alternating current, current will tend to concentrate on the surface of the wire flow. According to calculations, skin depth is related to frequency.
3. The Reason For Choosing The Gold Plating
In order to solve the above problems of the gold-plated plate, the use of gold-plated PCB has the following characteristics:
(1) Because of the different crystal structures formed by sinking gold and gold plating, sinking gold will be more yellow than gold plating, and customers are more satisfied.
(2) Because the crystal structure formed by gold plating and gold plating is different, gold plating is easier to weld, will not cause poor welding, or cause customer complaints.
(3) Because the gold plate only has nickel gold on the pad, the signal transmission in the skin effect is in the copper layer will not affect the signal.
(4) Because of the denser crystal structure of gold plating, it is not easy to produce oxidation.
(5) Because the gold plate only has nickel gold on the pad, so it will not be produced into gold wire caused by short.
(6) Because the gold plate only has nickel gold on the welding plate, so the welding on the line and the combination of copper layer is more firm.
(7) The project will not affect the spacing when making compensation.
(8) Because the gold and gold plating formed by the crystal structure is not the same, the stress of the gold plate is easier to control, for the products of the state, more conducive to the processing of the state. At the same time, because the gold is softer than the gold, so the gold plate is not the wear-resistant gold finger.
(9) The flatness and service life of the gold plate is as good as that of the gold plate.
4. Gilt Plating Vs Gold Plating
In fact, the plating process is divided into two kinds: One is electric plating, and one is sinking gold.
For the gilding process, the effect of tin is greatly reduced, and the effect of sinking gold is better; unless the manufacturer requires binding, most manufacturers will choose the gold sinking process now! In general, under common circumstances PCB surface treatment for the following: Gold plating (electric gold plating, gold plating), silver plating, OSP, spray tin (lead and lead-free), these are mainly for fr-4 or cem-3 plate, paper base material and coating rosin surface treatment; poor tin (poor tin eating) if the exclusion of solder paste and other patch manufacturers production and material process reasons.
Here only for PCB problem, there are the following reasons:
(1) During PCB printing, whether there is an oil permeating film surface on the pan position, which can block the effect of tin coating; can be verified by a tin bleaching test.
(2) Whether the pan position meets the design requirements, that is, whether the welding pad design can ensure the supporting role of parts.
(3) Whether the welding pad is contaminated, the results can be obtained by an ion contamination test; the above three points are basically the key aspects that PCB manufacturers consider.
The advantages and disadvantages of several ways of surface treatment are that each has its own advantages and disadvantages!
Gilding, it can make the PCB storage time longer, and by the outside environment temperature and humidity changes less (compared with other surface treatments), generally can be stored for about a year; spray tin surface treatment second, OSP again, these two surface treatment in the environment temperature and humidity storage time should pay attention to many.
Under normal circumstances, the surface treatment of sunken silver is a little different, the price is high, the preservation conditions are harsher, need to use non-sulfur paper packaging treatment! And the storage time is about three months! In terms of the tin effect, sinking gold, OSP, spray tin, and so on are actually similar, the manufacturer is mainly considering the cost performance!