Monthly Archives: April 2010

Why to use high Tg PCB Material?

Posted by on April 20, 2010 No comments

First of all, talk about the high Tg refers to the high heat resistance. With the rapid development of electronic industry, especially on behalf of computer electronic products toward the high function, high-rise development, require higher PCB material heat resistance as an important guarantee. With SMT, CMT represented by the emergence of high-density mounting technology and development, and the PCB in the small hole size, fine lines, thinner, the more inseparable from the support substrate with high heat resistance.

PCB materials under high temperature, not only produce softening, deformation, melting and other phenomena, but also in the mechanical, electrical characteristics of the sharp decline (I think we do not want to see their products occurred).

So the general high-Tg FR-4 and the difference between the FR-4: In the thermal state, especially in the heat after absorption, its materials, mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition , thermal expansion differences in various situations, high Tg products significantly better than the common PCB materials. This is why to use the high Tg PCB material.

PCB surface treatments

Posted by on April 14, 2010 No comments

Bare copper itself is very good solderability, but is easily exposed to air oxidation, and susceptible to contamination. This is also the PCB surface treatment must be the reason.

1. HASL
Hot-air solder leveling. The most common PCB surface treatment menthod. Lead and lead-free should be considered.

2. OSP
Organic solderability protective coating (OSP, Organic solderability preservative) is an organic coating to prevent oxidation of copper in the welding before, that is to protect PCB(printed circuit board) pad solderability from destruction.

3. ENIG
Nickel Immersion Gold. The copper surface is plated of Ni/Au. The deposition thickness of the inner Ni layer is generally 3~6um, the deposition thickness of the outer Au thin, usually 0.05 ~ 0.1um. Ni as the barrier layer between Cu and soldering tin. Welding, outside Au in the solder which melts rapidly with soldering tin and then turn into Ni/Sn intermetallic compounds with inner Ni. The gold-plated to prevent Ni oxidation during storage or passive, it should be enough gold plating density, the thickness can not be too thin.

4. Immersion Silver
Immersion silver process through the thin (about 0.1~0.4um) and dense to provide a layer of silver deposited organic protective film, the surface of the silver with the greatly extended life. Immersion Silver surface is very flat and very good with weldability.

5. Immersion Tin
Only used for two reasons for immersion tin process: first, the surface is very flat, coplanarity good; the other is lead-free. But in the immersion tine process easy to be with Cu/Sn intermetallic compound, Cu / Sn intermetallic is with poor solderability.

These are five main PCB surface treatments, since each have their own unique surface treatment technology, application is not quite the same.