As the integration of IC becomes higher and higher, the IC feet are more and more dense. However, it is difficult to flatten the thin pad by the process of straight tin injection, which brings difficulties to SMTmounting. The shelf life of extra tin-spray plate is very short. And the gold plating to solve these problems:
1, for the appearance of the mounting process, especially for 0603 and 0402 super SMAll table paste, because the flatness of the welding pad is directly related to the quality of the solder paste printing process, the back of the re burning welding quality plays a voting effect, so the whole plate gold in the high degree of density and super small table paste process from time to time to see.
2, in trying to make the stage, affected by the acquisition and purchase of components and other factors are often not the wrench to immediately welding, but often have to wait for a few weeks or even months to use, the shelf life of the gilded plate is many times longer than the lead tin alloy, so we are willing to think appropriate and use. In addition, the cost of gold-plated PCB circuit board in the sample stage is SIMilar to that of lead-tin alloy circuit board. But with more and more dense wiring, line width and spacing have reached 3-4MIL. Because this brings the problem of gold wire short circuit: as the frequency of the signal becomes higher and higher, the effect of skin effect leads to signal transmission in the multi-coating on the quality of the signal more superficial. Skin effect refers to: high frequency alternating current, current will tend to concentrate on the outer surface of the wire flow. According to the calculation, skin depth is related to frequency.
In order to solve the above problems of gold-plated circuit boards, it is considered appropriate to use gold-plated circuit boards of PCB mainly have the following unique places:
1. Because of the different crystal structure formed by sinking gold and gold plating, sinking gold will be more yellow than gold plating, and customers are more satisfied.
2. Because of the different crystal structure formed by sinking gold and gold-plating, sinking gold is easier to burn welding than gold-plating, which will not lead to bad welding and trigger customer complaints.
3, because the gold plate only has nickel gold on the pad, the skin effect of signal transmission is in the copper layer will not affect the signal.
4, because gold plating is more detaiLED and precise crystal structure, not easy to produce oxygen.
5, because the gold board only has nickel gold on the welding plate, so it will not be produced into gold wire lead to short.
6, because the gold plating circuit board only has nickel gold on the welding plate, so the welding and copper on the line is stronger.
7, the project will not affect the spacing initiation when making repayment.
8, because of the different crystal structure formed by gold plating and plating, the stress of the gold plating plate is easier to control, for the products of the state, more helpful to the processing of the state. At the same time, because the gold is softer than the gold, so the gold plate is not wear-resistant gold finger.
9, the flatness of the gold plate and the life of the gold plate is as good as the life of the gold plate.
So far, most factories have decided to use the gold sinking process to produce gold plates. However, gold sinking process is more expensive than gold plating process (gold content is higher), so there are still a lot of cheap products using gold plating process (such as remote sensing plate, tangram plate).For the gilding process, the effect of tin is greatly reduced, and the effect of sinking gold is better;Wrong not the manufacturer requirements is binding, otherwise most manufacturers will choose the sinking process! Common things under the condition of PCB appearance disposal for the following kinds of: gold plating (electric gold plating, gold plating), silver plated circuit board, OSP circuit board, spray tin (lead and lead free), these are mainly for FR-4 or CEM-3 board material, paper base material and coated resin appearance disposal form; On the tin is not good (eat tin is not good) if the removal of solder paste and other patch manufacturers production and material technology.
This is only for PCB circuit board problem, there are several reasons:
1. When printing pcb circuit board, whether there is oil permeating film surface on PAN position, it can prevent the effect of tin; This can be tested by a tin bleaching attempt.
2. Whether the moistening position of PAN position meets the preset requirements, that is, whether the preset welding pad can guarantee the supporting effect of parts.
3, the welding pad is not contaminated, which can be used to obtain the final result of ion pollution test;
On the appearance of the disposal of several forms of the lack of excellence, is each has its own advantages and disadvantages! Gold plating, it can make PCB storage place for a long time, and by the outside background temperature and humidity degree change is small (relative to other appearance disposal), generally can be retained for about a year; Secondly, the appearance of spray tin disposal, OSP again, these two kinds of appearance disposal in the background temperature and humidity degree of storage time should pay attention to a lot. Under the condition of ordinary things, the appearance of silver is somewhat different, the price is high, the retention conditions are more mean, the need to use non-sulfur paper packaging disposal! And the retention time is about three months! In terms of tin effect, sinking gold circuit board, OSP circuit board, spray tin and so on is actually similar!