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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


voids when waving

Views: 1917

coop

#48288

voids when waving | 9 March, 2007

I have recently been handed over the waving operation here, and am unclear on how to address our recent issue with our Wave. We are using AIM WS-715M Flux in a Foam fluxer, and are using AIM SN-100C in the wave. The problem is on several of the assemblies I am getting voids on the corner leads of IC's. The solder has a nice fillet on the solder side but isn't flowing to the component side at all. I have played with conveyor speed, air knife, pre-heater temp, wave temp, the gravity of the flux is within spec. so I just want to know what setting I can change to help this problem, is it heat,speed,height?

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#48327

voids when waving | 12 March, 2007

Have you checked the parts for contamination?

Are the voids out of spec?

IPC allows some voiding, especially with lead free solder. Component contamination can cause this to repeat, as well. Try pre-tinning the component in question, and see if suddenly you get better solder joints. Check the board for contamination, as well.

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#48328

voids when waving | 12 March, 2007

Questions are: * You say 'voids', but you describe poor barrel fill. Are you seeing both? * Sometimes designers need to reduce the heatsink effect of large ground and power places, but this usually shows on the two upper corner pins, not all corners. Are you seeing the barrel fill problem on all corners of the components? * What is the scope and distribution of this problem?

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coop

#48330

voids when waving | 12 March, 2007

I am aware of the IPC A-610 standards on acceptability of electronics, but this place builds our products to an even higher standard. the problem is on the two leading corners of the IC's as they go into the wave.

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george

#48331

voids when waving | 12 March, 2007

Are you using wave solder pallets? I use same flux and solder as you do. I've seen this problem when some walls in the wave fixture cause a "shadowing effect"...if you enlarge those openings you will increase the dwell time eliminatting voids (if the problem is not contamination-related)...

My two cents, George

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coop

#48336

voids when waving | 12 March, 2007

I am not using a solder pallet, I don't think the problem is contamination related, because these parts are on some of our other assemblies, and they're being waved with no problems. The problem seems to be mainly on our panelized boards for some reason. I have a feeling the problem I am encountering might be because the parts are being pre-formed, but the legs are not going straight down, they are at an angle thru the barrel. I think this might be all but plugging off the barrel. Slowing down the conveyor speed helped a little. I am going to try to preform some correctly and get the stuffing line to clip the leads shorter so I can decrease conveyor height and slightly decrease the wave's flow,making it less turbulent, hopefully this takes care of it, if not I guess it's time to look at the contamination of the pcb

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#48337

voids when waving | 12 March, 2007

Hi Coop,

Sounds like you are having top side wetting issues. Generally this is flux related, but with a foam fluxer, I'd kinda doubt it's the fluxer.

Could be heat related as well. Try slowing the conveyor speed to verify.

Long leads - hmmmmm. You may need to get you wave higher. But if all but two are soldering, I doubt this too. Do you have an Omega wave (electrovert) or some type of "chip wave"? This too can get solder to wick up to the top side.

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#48339

voids when waving | 12 March, 2007

That your problem is not related to component solderability or wave process related makes us believe this has to do with bare board design. Look at how your designer did the thermal relief on the two pins that don't solder well.

If you can't get a new copper pour to correct the thermal relief, preheat the blank out of these boards before soldering.

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coop

#48340

voids when waving | 12 March, 2007

Thanks to all for the input I will try the preheating the "blank" out of it too. the preforming Idea I had wasn't the problem. I'll slow down conveyor speed and increase the preheater temp.

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#48342

voids when waving | 12 March, 2007

Naw, lead forming is unlikely to be the source of the problem, because it only affected two leads.

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coop

#48346

voids when waving | 12 March, 2007

the problem must have been the ground plane like you were saying because I increased the preheater temp, slowed down the conveyor speed and they started looking better. Thanks to all for the input, especially davef. Thanks again

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