Why should the PCB board “paste gold”
PCB board surface treatment
Anti-oxidation, spray tin, lead-free spray tin, immersion gold, Shen tin, Shen silver, hard gold plating, the whole board gold-plated, Goldfinger, nickel palladium Gold OSP: the cost of the end, good solderability, storage conditions harsh, time Short, environmentally friendly technology, welding is good, smooth.
Spray tin: spray tin plate is generally multi-layer (4-46 layer) high-precision PCB model, has been a number of large domestic communications, computer, medical equipment and aerospace companies and research units can be used cheat (connecting finger ) Is the memory module and the memory slot between the connection components, all the signals are transmitted through the cheat.
Gold finger by the many golden conductive contacts, because of its surface gold and conductive contacts arranged like a finger-like, so called “cheat.” Gold finger is actually on the CCL through a special process and then covered with a layer of gold, because the strong antioxidant gold, and the conductivity is also very strong. But because of the high price of gold, the current more memory are used to replace the tin from the last century, 90 years began to spread the tin material, the current motherboard, memory and graphics cards and other equipment, “Goldfinger” is almost always used Tin material, only part of the high-performance server / workstation accessories contact points will continue to use the practice of gold-plated, the price is not cheap.
Why use gold plating
With the IC integration is getting higher and higher, IC feet are more and more dense. And the vertical spray tin process is difficult to fine into the pad flat, which SMT to the placement of the difficulty; the other spray tin plate life (shelf life) is very short. While the gold plate just solved these problems:
★ For the surface mount technology, especially for 0603 and 0402 ultra-small surface paste, because the pad flatness is directly related to the quality of solder paste printing process, the quality of the subsequent reflow to play a decisive impact, so the whole plate gold In high-density and ultra-small surface paste process often seen.
★ in the trial stage, by the component procurement and other factors are often not the board to the immediate welding, but often have to wait a few weeks or even a month to use, gold plate life expectancy (shelf life) than the lead Alloy long times so much we are willing to adopt. Moreover, the cost of gold-plated PCB in the sampling phase compared with the tin alloy plate is almost the same.
But with the wiring more and more dense, line width, spacing has been to 3-4MIL.
So the problem of wire short circuit: With the signal frequency is getting higher and higher, due to skin effect caused by the signal in the multi-coating transmission of the signal quality of the more obvious.
The skin effect refers to: high frequency alternating current, current will tend to focus on the surface of the wire flow. According to the calculation, skin depth and frequency.
Why use the sink plate
To solve the above problems of gold-plated plate, the use of Shenjin plate PCB has the following characteristics:
★ due to immersion gold and gold plating formed by the crystal structure is not the same, Shen Jin will be golden gold is more yellow than gold, customers are more satisfied.
★ due to immersion gold and gold formed by the crystal structure is not the same, Shen Jin is more easy to weld than gold, will not cause poor welding, causing customer complaints.
★ because the sink plate only gold on the pad, the skin effect of the signal transmission in the copper layer will not have an impact on the signal.
★ because the gold plate only gold on the pad with gold, so it will not produce gold wire caused by short.
★ because the sink plate only gold on the pad, so the line of solder and copper layer of the combination of more solid.
★ works in the compensation will not have an impact on the spacing.
★ due to immersion gold and gold plating formed by the crystal structure is not the same, the pressure of the gold plate easier to control, for a bonding of products, the more conducive to the bonding processing. But also because the gold-plated gold than gold, so the gold plate to do the gold finger is not wearable.
★ Shen Jin plate flatness and standby life and gold plate as good.
Shen gold plate VS gold plate
In fact, gold-plated process is divided into two kinds: one for the gold plating, one for the immersion gold.
For the gold-plated process, the effect of tin on the greatly reduced, and the immersion gold on the tin effect is better; unless the manufacturers are required to bind, or now most manufacturers will choose the immersion process! Commonly used cases of PCB surface treatment for the following: gold-plated (gold plating, immersion gold), silver, OSP, spray tin (lead and lead), these are mainly for FR-4 or CEM-3 Such as the plate, the paper base is also coated with rosin surface treatment; on the tin bad (eat tin bad) this piece if the exclusion of solder paste and other chip manufacturers production and material technology reasons.
Here only for the PCB problem that there are several reasons:
★ in the PCB printing, PAN bit on whether there is oil film surface, it can block the effect of tin; This can be done to test the tin test.
★ Does the position of the PAN bit meet the design requirements, that is, whether the pad design is sufficient to ensure the support of the part.
★ pad there is no pollution, which can be used to test the results of ion pollution; the above three points is basically the focus of PCB manufacturers to consider.
On the surface treatment of the advantages and disadvantages of several ways, each has its own strengths and weaknesses!
Gold plating, it can make PCB storage for a long time, and by the outside environment, the temperature and humidity changes smaller (relative to other surface treatment), the general can save about a year; spray tin surface treatment Second, OSP again, this Two kinds of surface treatment in the ambient temperature and humidity storage time to pay attention to many.
Under normal circumstances, Shen silver surface treatment is a bit different, the price is high, more stringent preservation conditions, the need for non-sulfur paper packaging treatment! And save time in about three months! In terms of tin effect, the immersion gold, OSP, spray tin, etc. is actually about the same, manufacturers mainly consider the cost-effective aspects!