Hi Victor

Before answering your question I want to understand your process and problem more clearly.

1. What is the type of nickel finish? For exanple:

A. ENIG (electroless nickel immersion gold)
B. Electroplated nickel and gold.
C. Other (explain)

2. What is the thickness of the nickel and gold layer? 

3. What is the soldering process (assume paste + IHR reflow) and solder alloy composition.

4. Do you notice any discoloration of the gold surace before processing? 

5. After soldering, when the defective solder joint is lifted, what is the surface condition of the nickel pad? For example:

A. Some solder remains (partly wetted)
B. Some solder and gold remains
C. No solder and the nickel surface is dark colored
D. Some nickel is removed and copper exposed.

6. Is the weak solder joint a general problem for all pad sizes or limited to smaller pads (for example, BGA 0.8mm or smaller)?

7. In general, soldering nickel can have several problems:

A. The wetting properties of nickel are poor in comparrison to copper and it wets more slowlly (wetting is more heat and time dependant). You may have to use a different reflow profile than with other finishes.
B. Nickel passivates (oxidizes) rapidly so the purpose of the gold is to protect the nickel and if quality is good the gold dissolves and a tin-nickel intermetallic wil form as the nickel wets. However, if the nickel is oxidized poor wetting or no wetting may result. 
D. Various nickel or gold problems could contribute to the problem including porous of thin nickel, too thick/thin gold, surface contamination etc. You should inspect some unprocessed PCBs to look for obvious signs of discoloration or contamination, ans measure the plating thickness confirming compliance to spec.

8. Photos of the defect would be helpful.

Regards,

C.B. Katzko
by Blackberry


----- Original Message -----
From: victor [[log in to unmask]]
Sent: 08/30/2008 10:41 AM ZE8
To: [log in to unmask]
Subject: [TGA] Soldering Nickel on PCB





Hi Friends,

 

Here is my concerns about the soldering of nickle. Pls share your valuable knowledge and experience with me.

 

1. How to judge the strength of solder joint of nickle with lead-free solder? Any spec?

 

2. What can  I do if I found the solder joint  of nickel tab is not strong enough?(The soldered nickel tab is very easy to fall off when you peel it.)

 

Thanks,

 

Victor