Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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Scott J

#10114

De-wetting | 17 August, 1999

Can anyone help on the subject of de-wetting during the spray coating process. We use PC29M Parts A+B spray coating material, Humiseal tapes and masking dots, Marigold supertouch V70N gloves and Concoat CM533 liquid masking material. We also use a Kolb RB4DSE aqueous cleaning system prior to masking and the boards are tested for ionic contamination. I recently spent time upgrading housekeeping practices as I thought contamination was being passed onto the PCB's through operator handling during the masking process due to de-wetting patterns found on some PCB'S. The occurance of the de-wetting seems to be random, the boards are prepared for coating on both day and night shift.

Any Thoughts !

Thanks in advance

Scott J

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Brian

#10115

Re: De-wetting | 17 August, 1999

| Can anyone help on the subject of de-wetting during the spray coating process. We use PC29M Parts A+B spray coating material, Humiseal tapes and masking dots, Marigold supertouch V70N gloves and Concoat CM533 liquid masking material. We also use a Kolb RB4DSE aqueous cleaning system prior to masking and the boards are tested for ionic contamination. I recently spent time upgrading housekeeping practices as I thought contamination was being passed onto the PCB's through operator handling during the masking process due to de-wetting patterns found on some PCB'S. The occurance of the de-wetting seems to be random, the boards are prepared for coating on both day and night shift. | | Any Thoughts ! | | Thanks in advance | | Scott J | Scott

Are you using any form of abrasives at any point? My experience shows that surface contamination more frequently causes non-wetting, but implanted abrasive particles are hell for dewetting, especially into copper.

Brian

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Brian Wycoff

#10116

Re: De-wetting | 19 August, 1999

| | Can anyone help on the subject of de-wetting during the spray coating process. We use PC29M Parts A+B spray coating material, Humiseal tapes and masking dots, Marigold supertouch V70N gloves and Concoat CM533 liquid masking material. We also use a Kolb RB4DSE aqueous cleaning system prior to masking and the boards are tested for ionic contamination. I recently spent time upgrading housekeeping practices as I thought contamination was being passed onto the PCB's through operator handling during the masking process due to de-wetting patterns found on some PCB'S. The occurance of the de-wetting seems to be random, the boards are prepared for coating on both day and night shift. | | | | Any Thoughts ! | | | | Thanks in advance | | | | Scott J | | | Scott | | Are you using any form of abrasives at any point? My experience shows that surface contamination more frequently causes non-wetting, but implanted abrasive particles are hell for dewetting, especially into copper. | | Brian | I have run into this problem before. What kind of solder mask is on the boards? We had a customer who used dry mask, and it was a you-know-what! If it's not dry mask, are you baking the boards prior to coating? How are you curing the coating? Sometimes the adhesion of coatings is affected by moisture in the board surface evaporating during a heat cure. The test for ionic contamination may not catch some of the other types of contaminant, such as glycols (dry mask process, or the moisture in the board surface. Solutions: For the dry mask, we had to measure the boards coming in to catch any hint of poor processing of the dry mask solder mask. For moisture in the board surface, we would clean the boards, then bake them for 2 to 4 hours at 190 degrees F. then move them immediately to mask and coat. If the boards would not make it thru those processes that way (like before a weekend or holiday, we would rebake the boards or not even start them until they could get through both processes.

good luck. Hope this helped.

Brian Wycoff

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