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Whitish Solder Joint



Whitish Solder Joint | 4 April, 2003

we recently detected white colour solder joints, across the whole board. we tried to clean with IPA but without effective return of solder joint to shiny joints. Anyone has any ideas on how this post-SMT reflow solder joint could have changed to whitish joint? we use water souble paste with Aqueous Cleaner >10Mohm DI washing.

On the paste supplier recommendation, we sent sampling boards for Ionic Contamination test with specs <14NaCl/Sq.inch. We find the results not satisfactory to give any confidence in functional cleaniness of the boards.

Reason is boards with really HEAVY white residue (almost crystal like) can still pass the Ionic contamination test with reading of 11.1NaCl/, whereas boards with faint traces of white in the solder joint (only) itself reads as 19.2NaCl/sq.inch. Any comments from experienced qualifiers of such Ionic contamination tests to gain customer confidence that white residue on board is acceptance?

We referrence to IPC-A-610C (section 6.1) and it says as long as solder fillet is concave and meets the solder fillet acceptance criteria (slope/smooth skin surfaces/geometric volumes fusion to PCB/terminals) the solder fillet colour is irrelevant? On the other hand under cleaniness section 7.3 of IPC-A-610C, says no white residues is allowed? Any comments on which takes priority in acceptance critera, from the more experienced and/or wiser folks, pls?

Thanks in advance to the replys, appreciate the help!

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Kevin Facinelli


Whitish Solder Joint | 4 April, 2003

What paste are you utilizing?

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Whitish Solder Joint | 4 April, 2003

Q1: Anyone has any ideas on how this post-SMT reflow solder joint could have changed to whitish joint? A1: Dunno. You need to tell us more. For instance: * What is the appearance of this white residue? [eg, glassy / coarse, milky colored / opaque, thin / thick film, hard / soft, color white, etc] * Where are these white residues located? [eg, pads only, solder mask only, every where, etc.] * What is the scope and extent of the problem? * What is your process, process materials, board fabrication, and process settings?

Q2: Why do some white residues pass ionic contamination tests and other white residues do not pass? A2: White residues are chemical compounds. Chemical compounds can be either ionic or nonionic. Ionic contamination testers only measure ionic compounds.

Q3: What can I tell my customer to make them feel comfortable about these white residues? A3: Tell them you plan to send the boards to a contract shop for cleaning and testing to assure that their boards absolutely immaculate.

Q4: What takes precedence to IPC-A-610C, 6.1 or 7.3? A4: Neither takes precidence. White residues are unacceptable, because they indicate a process that�s not well controlled.

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Whitish Solder Joint | 4 April, 2003

Do you reflow both sides of the boards before washing? Sometimes these white residues occur from "burnt" flux. we see this from time to time especially when using hot air and liquid flux.


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Whitish Solder Joint | 4 April, 2003


Did you use this paste before with out any problem or is it occuring for the first time ?

If you wash only once a double sided board the side that passes through two reflow will have hardened flux which will may not be washed in your normal washer.

What is the temperature and time of your reflow? If you overcook the residue, again then it will not be washable.

good luck

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