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SMT electronics assembly manufacturing forum.


White residues


RDR

#19628

White residues | 22 April, 2002

Greetings All, Anybody out there experiencing white residues after cleaning? We currently use a batch cleaner to clean water soluble fluxes. this cleaner makes its own DI water by means of carbon and resin tanks. After cleaning there are residues on all of the solder joints. They can be brushed off but will not come off with subsequent washing with either alcohol or water. We have tested the boards with an IONOGRAPH and the level is good but customers don't like it much and neuther do I for that matter.

Any help greatly appreciated!

Russ

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#19629

White residues | 22 April, 2002

Lots of good info on this subject in the SMTnet forum archives. Please search on your topic.

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ianchan

#19634

White residues | 22 April, 2002

Hi,

this is not really a technical solution, just a feedback.

we too have a model series using the same WS paste type. it gives a dull solder joint with white residue that can be marginally removed after post-DI water rinse (ie. not 100% removed).

We flipped thru our IPC-A-610C and reversed analysis our process flow for the product. till today we can't eliminate 100% the occurrence of white residue on solder joints, nor improve the solder joints into "target" IPC specs of bright shiny solder joints.

what all this effort did help with, is that some level of compromise is possible to achieve if we know the inherent characteristics of the direct raw materials that is incorporated into building the assembly board.

We believe (based on what we know of the intended paste operational condition, from the Tech-Sheet) is that we do have a longer than normal reflow time & peak temperature, to accomodate the leadless chip carrier (LCC) solder wetting onto bare LCC copper terminals. Its all still within paste specs, but more to the extreme higher side of the paste supplier Tech-Sheet "recommended" profile.

The paste supplier advocates reducing the peak temperature to prevent the white residue from occurring. As we need that 1st Pass Yield for LCC terminals wetting (its a 20mils pitch IC package) to minimize manual soldering touchup, we live with the "lesser evil" of white residue.

Thing is, anyone who has solution to share with us, is much appreciated for your sharing with us all. Thanks in advance.

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#19635

White residues | 22 April, 2002

Buy different paste.

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#19636

White residues | 22 April, 2002

Russ: What is the composition of this non-ionic material on your pads?

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ianchan

#19640

White residues | 23 April, 2002

would like to do a paste change, yet this paste was defined by the end-end-customer. this makes it one heck of a ECN paper trail just to start the evaluation DOE of new paste for this *customer project* group. ah, the politics of working life... wonder how dilbert would respond?

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CFraser

#19644

White residues | 23 April, 2002

I too have experienced this problem on many occasions. Try turning you wave temperature down just a bit. If you spec allows for this it will help. The condition will not totally go away but reducing the heat will help. Of coarse you other option in a no-clean process.

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RDR

#19652

White residues | 23 April, 2002

We have not yet sent this out for analysis, So, I don't really know what it is. initial evaluation would lead me to believe that it is flux since it is only present on the solder joints themselves and nowhere else. I noticed that you also mentioned to change paste. I have been wondering about that. I have used this paste for quite a few years with no problems (it is brand A WS609). but we used to use big in-line cleaners with saponafiers and detergents. Next time I post I will make sure that I do the up front work first. I was hoping a cleaner manufacturer might respond also?

Russ

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#19677

White residues | 24 April, 2002

We�ve been using WS609 for a long time, also.

Life or death based on what you�ve said? Choices are: * Wash water is too hot >50�C. * Boards are too hot to be cleaned.

Yes, saponified cleaners will remove heat decomposed WS flux.

Well, I suggested changing paste to another poster, because he mentioned overheated solder connections and I guessed that his white residue was heat stressed flux.

If you do too thorough a job with up-front work, we won�t be able to talk to you.

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Mr.T

#19715

White residues | 29 April, 2002

Hi,

That is very common in WS pastes.It is white residue (Salt) Usually it�s not dangerous it only looking bad.

I think best way would be contact your paste supplier and they should know what would take a stain off if not, change supplier.

There is water soluble which is 100% water soluble and you just wash it with ionic water or just water.You could also try Surpclean from Microcare it is good but expensive.We use that.This still does not solve your problem that you have to clean boards by hand.

Good luck Regards,

MadReindeer

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#19720

White residues | 29 April, 2002

MadReindeer

If this white residue is salt, * Why do you say is the presence of it 'not dangerous it only looking bad'? Don't salts sometimes go into solution with moisture on the board from humidity in the air and form cathodic plating shorts between leads on the board? * Why doesn't it go into solution when washed? Salts usually love to dissolve into water. * Why doesn't it go into solution in the Ionograph? Salts usually love to dissolve into water and IPA mixtures. * Why doesn't it show-up in the Ionograph reading? The cell on the Ionograph is designed to measure dissoved halogens.

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Jim M.

#19725

White residues | 29 April, 2002

I had problems with white residues on both WS609 and WS 3060.The WS 3060 turned out to be a carbonized material.The composition after analysis (Energy Dispersive X-ray spectrum) turned out to be tin,tin,phosphore and cloline and tin.

Alpha also have a technical paper on their website called White residue and water soluble fluxes:http://www.alphametals.com/products/solder_solutions/pdf/White%20Residues%20%20Water%20Soluble%20Fluxes121900.pdf

I tried everything to get rid of white residue without success.(i have an inline DI cleaner usually running between 120F-135F) Finally qualified another solder paste and no more white residue.

Jim M.

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