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White Flux Stains - stubborn stains

ianchan

#18685

White Flux Stains - stubborn stains | 19 January, 2002

Hi,

Have a board run, using 63/37 Water Souble (WS) process. during the reflow setup time, we had unsolder issues on a leadless bump chip carrier (BCC) IC level package. To rectify the unsolder rejects, we adjusted the reflow time from 25-55sec into a 64sec. This reflow adjustment helped solve the unsolder issues. (night shift).

Unfortunately, the next day (morning shift), we found white coloured "spider-web" looking flux stains on the solder joints. The supplier attributed the web flux stains to our high reflow time and the small pcba size. The stains look like a spider-web, as it has "bubbles" occuring during the high reflow time; and it only readily visible under 30x scope magnification, scope inspection dictated by the customer...

We tried using IPA, prozone, and 60-80(deg-C) hot water to brush the white flux stains. All these efforts only helped to reduce some of the flux stains...

Anyone have some recommended flux stain removers, for us to further try this "polish touchup" of the flux stains? Or anyone have experience in similar issue, and managed to get customer conditional acceptance on such flux stains?

In advance, Everyone's experience shared and engineering advice, on this migraine, is greatly appreciated, Thanks!

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CPI

#18734

White Flux Stains - stubborn stains | 28 January, 2002

Did you perform a cleanliness test on the boards? did it pass? if yes whats the issue? visual attributes like this will not effect form fit or function of the device. Finding this under 30X, wow, why 30X????

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Mr.T

#18778

White Flux Stains - stubborn stains | 1 February, 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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