| Hi folks, | | I am looking for inputs on a long-standing problem encountered in our shop: Bottom-side parts (passives) falling off in the Wave...where the only remnants of the part is a flattened glue dot of proper diameter and volume, and sometimes flux residue (from the wave). |
hi Marc.
Ah.....an age old problem. Really tough to pin down. Have you definitely pinned the missing passives down to the wavesolder work center? or is that just where you find the problem?
We've all experienced missing bottomside parts over the years. How thin is your substrate, and what mat'l is it? .031 teflon is lots harder to handle properly than .062 FR4. Here's something to try......
mid day, go out and walk the line. Start at ICT, and work backwards--through post wave ass'y, touchup / rework, cleaning (if you have the process), wave, and all areas in between the placement of the passives and the end of the process.
My money says hands down that in addition to a possible chemistry problem (which I've never experienced), you have a handling issue. Manual or conveyor....it IS there. Look inside the entrance and exit end of your cure oven. Look under tech benches, metro carts, conveyors, etc. Check trash cans from where the operators have swept up and dumped.
I have even observed passives go flying at the entrance and exit end of an in-line cleaner--they get pinched between the idler and drive sprockets and the wire belt links of the wire belt conveyor. No kidding. Check me out on this.
I found that by enforcing good handling disciplines, ensuring positive displacement pumps in good order, no air in glue / lines, and good glue (and ensure it's within the mfg'er's shelf life)......combined with buying brand new placement gear......my #1 defect on the floor virtually disappeared. BTW, I used Loctite 3609 with Camalot dispensing gear. Tried the Amacon yellow stuff, as well. Worked OK.
Please let us know what you find.
Scott Cook
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