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Wave Solder - solder bubbles/outgassing??

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Brandon

#45042

Wave Solder - solder bubbles/outgassing?? | 14 November, 2006

Hello all, I am having an issue with some boards on our Wave Solder. It is a Pb free wave and These particular boards are exibiting A LOT of what I call solder bubbles in the larger than usual vias and un-used thru holes. Settings: 4 inch/min 144c topside preheat temp before reflow 275c Solder pot temp 3 sec of solder contact time

The profile looks good to me. We are spraying on the water soluble flux with a spray bottle. There is an excessive amount. Although I have tried spraying the least I could by holding the spray nozzle 1 foot away from the board while spraying.

When the Board comes out it has huge solder bubbles in the vias and un-used thruholes. These are bubbles not solid solder. You can puncture the bubble and open it up to reveal a hollow barrel. The bubbles are on both the top and bottom side of the boards. I don't think an air knife will have any effect to cure this. Ours is broken anyway. I tried baking 4 boards at 100 + celcius for 5 hours and then running them. Same problem. No improvement. I am at a loss. Can anyone help me out here? I thought it must be moisture, but it doesn't seem to be the case. I thought it might be flux outgassing, but we tried 4 different fluxes one was even No-Clean and we got the same results. That makes me think it is the boards. We run other boards using the same exact perameters and they look beautiful. That makes me think it is the boards. Are there board house defects that could cause this? Design issues?

Thanks, Brandon

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RDR

#45044

Wave Solder - solder bubbles/outgassing?? | 14 November, 2006

You have incomplete plating in the through holes would be my bet, baking will not solve, nothing will, at least that is what I have found except a lot of hand work and frustration, have your PCB house perform cross section at affected area in your presence.

Russ

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Brandon

#45214

Wave Solder - solder bubbles/outgassing?? | 17 November, 2006

Thanks Russ. I have contacted the board house. Will post results later.

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#45250

Wave Solder - solder bubbles/outgassing?? | 17 November, 2006

OK, why are you hand fluxing? You may want to take the time to use your real fluxer. Yeah, it's a bit messy but you can control the amount of flux you're putting on the board. And with water based fluxes, this is critical. If you are stuck to hand fluxing, try some other fluxes to see of you get the same results.

Oh yeah, trade in your hot air knife and get an Omega wave put in!

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rob@spinpcb.com

#45251

Wave Solder - solder bubbles/outgassing?? | 17 November, 2006

What kind of board finish do you have?

You describe solder bubbles...and when you remove them, you find open vias. Are you, by chance, discovering flux contained in these bubbles?

We've been experiencing the same thing with pb-free soldering on a static solder pot. Both light and heavy hand flux application have given us the same result...mostly on white-tin boards. Boards with an ENIG finish don't seem to give us these results.

If you are using white-tin, I've been advised that cleanliness is key with the white-tin finish. I haven't performed any experiments with my problems yet, as I don't have a job to run at the moment. I'm trying to convince my customer to switch to ENIG.

..rob

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greg york

#45336

Wave Solder - solder bubbles/outgassing?? | 21 November, 2006

Had exactly the same problem the other week. Baked some boards did improve slightly but not convincingly. Washed bare PCb and found excessive HASL fluids left on board from improper rinsing and problem disapeared. Baking HASL fluid out is impossible it needs rinsing out and it is very hygroscopic. Also seen similar with Au/Ni and Ag finish but this was improper developing leaving residue of resist down the holes Try rinsing bare PCB with HOT water not cold. I think some wetters used could be gelling up when hit with cold water causing the issue Please let me know how you get on. Also Cu thickness needs to be higher as well around 25 micron I believe due to extra heat required and longer dwell time in bath some solders non SAC require dwell time of 4 - 5 seconds very long time. some people believe SAC problem is due to SAC dissolving copper quicker I dont personally believe this is true I think it is just temp over time in dwell of solder with thin plating of copper in through holes and laminate boiling out through the holes. We manufacture solder and it takes forever to dissolve Copper into the Tin/Silver mix even when operated around 350C. Cheers Greg York

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