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Printed Circuit Board Assembly & PCB Design Forum

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non-wetting on gold land pad

chris

#8782

non-wetting on gold land pad | 27 October, 1999

Hi

What is the possible cause of non-wetting of solder paste to the gold land pad. What we observed in the surface of the non-wet pad is an organic FM, and using FTIR we found out that it is a flux. It is possible that the cause of non-wetting is the flux residue. What other factors may cause non-wetting.

regards

Chris

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#8783

Re: non-wetting on gold land pad | 28 October, 1999

Chris: Typical non-wetting causes are:

* Poorly controlled soldering process * Incorrect material * Surface contamination * Insufficient preheat * Misapplied solder mask * Shadowing

Without intending to insult you, all of the causes of non-wetting, poor wetting, and dewtting are not the same.

Tell us how you observed the organic FM on the board and why you like FTIR for analyzing surface contaminants.

Ta

Dave F

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chris

#8784

Re: non-wetting on gold land pad | 28 October, 1999

Hi Dave,

We suspect that the organic FM causes the non-wetting problem. FTIR analysis confirm that the FM is a flux residue. Dave we only used FTIR to detect organic contaminants, we also used SEM/EDX to determined the elemental composition of the failing land and so far no significant element was found using this tool.

What do you mean by shadowing?

regards Chris

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#8785

Re: non-wetting on gold land pad | 29 October, 1999

Chris: Thanks.

SMTnet has a "Library." Buried deep within it is a listing of terms. The following is from that listing:

Shadowing. When a component blocks the heat or solder wave flow from certain areas of the printed circuit board, resulting in incomplete soldering.

Ta

Dave F

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#8786

Re: non-wetting on gold land pad | 29 October, 1999

Chris A lot of people have reported sudden, fab lot related problems with Ni/Au pads. These are usually characterized by a discoloration of the gold and called cheerful names like "black pad disease". This can be a process problem at your fab house relating to the phosphorus level in the Ni bath or the porosity of the Au plating. The non/dewetting will usually occur over the whole surface of the fab rather that on just a few pads. Search the archives for more. good luck John Thorup

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chris

#8787

Re: non-wetting on gold land pad | 4 November, 1999

Hi John,

Thanks to your reply, just one question is it possible that the solder paste ( flux material )applied to the pads cause the non-wet.

regards

Chris

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#8788

Re: non-wetting on gold land pad | 5 November, 1999

Chris: You can have more than "one question!!!"

Anyhow, yes crappy solder paste can cause non-wetting, but before you go there understand why the paste is wetting some surfaces, but not others.

Ta

Dave F

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