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White Residues

Views: 1585

Peter

#36132

White Residues | 16 August, 2005

Hello,

I have a question on white residues formation at wave soldering. We have recently run experiments to test the performance of various halide-free water soluble fluxes (ORH0 under JSTD-004). The flux was applied through a spray fluxer and all PCAs were immediately washed after wave soldering in in-line cleaner, with DI water only.

Surprisingly, we've identified several PCAs built with flux A from one vendor exhibiting white residues at various T/H leads on the boards. See images below.

http://members.shaw.ca/ppwlee1/Images/White_residues1.JPG

http://members.shaw.ca/ppwlee1/Images/White_residues2.JPG

What could be the cause and forming mechanism of the residues? What causes it to become (sometimes) insoluble in water? In general what approach can be taken to minimize or prevent formation of white residues?

Rgds, Peter

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#36133

White Residues | 16 August, 2005

Hi,

Are they no clean fluxes?

Regards,

Grant

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#36135

White Residues | 16 August, 2005

Peter: Questions are: * From your pictures, the white residue appears to be only on the solder mask. Is that correct? If not, what is the location [eg, solder, nonsolder/nonmask areas] of the residue that doesn't show well in the pictures? Further, is this strictly a second-side problem? * You say that the white residue appears after washing, what temperature were the boards when washed? What was the wash temperature? * You say that the white residue appears after washing, what have you noticed that is peculiar in post-wave inspection? * When you say, "we've identified several PCAs built with flux A", what is the distribution [eg, lot, on the board] of the problem? * What is your analysis of the make-up of the white residue?

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RDR

#36136

White Residues | 16 August, 2005

It appears that the flux was burnt over the wave process. I have seen this before. Are you using convection heat?

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#36140

White Residues | 16 August, 2005

Hi Peter, I posted these links to Technet as well, but figured I would add them here as well in case any of the smtnet readers would like to see them. Here are some links to some articles about white residue sources, and whether or not white residues are good or bad. Contact our company offline if you want more specific advice to your situation.

Here are the links: http://www.residues.com/pdf/processRx_6-04.pdf http://www.residues.com/pdf/white_residue1.pdf http://www.residues.com/pdf/white_residue2.pdf

Regards, Sara

Foresite Inc. (765)457-8095 www.residues.com

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#36158

White Residues | 17 August, 2005

Dave,

Answers to your questions:

* From your pictures, the white residue appears to be only on the solder mask. Is that correct? If not, what is the location [eg, solder, nonsolder/nonmask areas] of the residue that doesn't show well in the pictures? Further, is this strictly a second-side problem?

The areas with noticeable white residues were on solder side, solder mask only, and around all T/H leads.

* You say that the white residue appears after washing, what temperature were the boards when washed? What was the wash temperature?

Boards were at ambient temp (20-23C) before wash. Wash&Rinse cycle 8min at 130F in DI water, Dry 2 min at 100F

* You say that the white residue appears after washing, what have you noticed that is peculiar in post-wave inspection?

Nothing that jumps out as far as residue flux amount and appearance go.

* When you say, "we've identified several PCAs built with flux A", what is the distribution [eg, lot, on the board] of the problem?

We ran tests to compare performance of 5 different fluxes, same setup and pcb lot. One flux came out with this problem.

* What is your analysis of the make-up of the white residue?

In-house Ionograph test passed with low readings. Ion chromatography results were excellent.

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Kris

#36162

White Residues | 17 August, 2005

What is the surface finish of the board ? Some flux are known to react with certain type of board chemistry.

Have you verified the compatibility of your solder mask and flux ?

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#36164

White Residues | 17 August, 2005

As others said, it appears that this mask and than flux are not compatible.

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