Views: 0 Author: Site Editor Publish Time: 2024-05-16 Origin: Site
I. PCB board surface treatment：
Antioxidant, tin spraying, lead-free tin spraying, immersion gold, immersion tin, immersion silver, hard gold plating, full-board gold plating, gold finger, nickel-palladium gold OSP: lower cost, good solderability, harsh storage conditions, short time, environmentally friendly process, good soldering, flat.
Tin spray: tin spray board is generally multi-layer (4-46 layers) high precision PCB prototype, has been a number of large domestic communications, computers, medical equipment and aerospace enterprises and research units can be used gold finger (connecting finger) is a memory stick and memory slots between the connecting parts, all the signals are transmitted through the gold finger.
The golden finger consists of many golden coloured conductive contacts, because its surface is gold plated and the conductive contacts are arranged like fingers, so it is called "golden finger". Gold finger is actually in the copper-clad board through a special process and then coated with a layer of gold, because of the strong oxidation resistance of gold, and conductivity is also very strong. However, because of the expensive price of gold, more memory are currently used instead of tin-plated, tin material from the 1990s began to spread, the current motherboard, memory and graphics cards and other equipment, "Gold Finger" is almost always used in the tin material, only some of the high-performance servers / workstations will continue to use gold-plated parts contact points! Practice, the price is naturally expensive.
Second, why use gold-plated boards
With the increasing integration of IC, IC feet are more and more dense. Vertical tin spraying process is difficult to become a fine pad blown flat, which brings difficulty to the SMT mounting; in addition to the tin spray board to be used life (shelf life) is very short. And gold-plated plate just to solve these problems:
1, for the surface mount process, especially for 0603 and 0402 ultra-small table sticker, because the pad flatness is directly related to the quality of the solder paste printing process, the quality of the latter reflow soldering to play a decisive role in influencing the quality of the whole board, so the whole board gold-plated in the high-density and ultra-small table sticker process is often seen.
2, in the trial stage, by the impact of factors such as component procurement is often not the board to immediately weld, but often have to wait a few weeks or even months before using the gold-plated board to be used life (shelf life) than the lead-tin alloy many times longer, so we are happy to use. Plus gold-plated PCB in the degree of sample stage of the cost of lead-tin alloy boards compared to the difference.
But with the wiring more and more dense, line width, spacing has reached 3-4MIL.
Therefore brings the problem of gold wire short circuit: with the signal frequency is higher and higher, due to the skin effect caused by the signal in the multi-layer plating in the transmission of the situation on the signal quality of the more obvious.
The skinning effect refers to the fact that with high frequency alternating currents, the current tends to concentrate on the surface flow of the wire. According to the calculation, the skinning depth is related to the frequency.
Third, why use immersion gold plate：
In order to solve the above problems of gold-plated boards, the PCB with immersed gold has the following main features.
1, because the crystal structure formed by immersion gold and gold-plated is not the same, immersion gold will be gold-coloured more yellow than gold-plated, customers are more satisfied.
2、Because the crystal structure formed by gold immersion and gold plating is not the same, gold immersion is easier to weld than gold plating, which will not cause welding defects and cause customer complaints.
3, because of immersion gold plate only pads on the nickel gold, skin effect in the transmission of the signal is in the copper layer will not have an impact on the signal.
4, because of the immersed gold crystal structure is more dense than gold-plated, not easy to produce oxidation.
5, because of the immersed gold plate only pads on the nickel gold, so will not produce gold wire caused by micro-short.
6, because of the immersion gold plate only pads on the nickel gold, so the line solder resistance and the combination of copper layer is more solid.
7, the project will not have an impact on the pitch when making compensation.
8, because of the immersed gold and gold plating formed by the crystal structure is not the same, its immersed gold plate stress is easier to control, for products with bonding, more favourable to the processing of bonding. At the same time, it is also because of the immersed gold is softer than gold-plated, so the immersed gold plate to do the gold finger is not wear-resistant.
9, immersed gold plate flatness and to be used life as good as gold-plated plate.
IV. Immersion gold plate vs gold-plated plate：
In fact, the gold-plating process is divided into two kinds: one for the electroplating, one for the sunken gold.
For the gold-plated process, the effect of tin on the greatly reduced, and the effect of immersion gold on the tin is a little better; unless the manufacturer's requirements are bound, or now most manufacturers will choose the immersion gold process! Generally common PCB surface treatment for the following: gold-plated (gold-plated, gold-plated), silver-plated, OSP, spray tin (leaded and lead-free), these are mainly for FR-4 or CEM-3 and other boards, paper-based materials and coated with rosin surface treatment; on the tin is bad (eat tin is bad) this piece of if you exclude the solder paste, such as the patch manufacturers of the production and material process reasons for this.
Here only for the PCB problem said, there are several reasons:
1, in the PCB printing, PAN bit on whether there is oozing oil film surface, it can block the effect of tin; this can be done to verify the drift tin test.
2, PAN bit of the wetting bit on whether or not to meet the design requirements, that is, whether or not the pad design can be enough to ensure that the role of the support of the parts.
3, the pad has not been contaminated, which can be used to test the results of ionic contamination; the above three points are basically PCB manufacturers to consider the key aspects.
About the advantages and disadvantages of several ways of surface treatment, is each has its own strengths and weaknesses!
Gold-plated, it can make the PCB storage time is longer, and by the external environment temperature and humidity changes are small (relative to other surface treatment), generally can be saved for about a year; spray tin surface treatment, followed by OSP again, the two surface treatment in the environment temperature and humidity of the storage time to pay attention to many.
In general, sinking silver surface treatment is a little different, the price is also high, preservation conditions are more demanding, need to use sulfur-free paper packaging treatment! And the preservation time in about three months! In terms of tin effect, immersion gold, OSP, spray tin, etc. is actually almost the same, the manufacturer is mainly to consider the cost-effective aspect!
