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How to reduce solder joint voids of LED without using vacuum reflow?

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SMTA-Rogers

#82491

How to reduce solder joint voids of LED without using vacuum reflow? | 6 May, 2019

Hello! Do you have a better stencil design to reduce the large area of solder joint voids? Or is there a suggested way to set the reflow profile? Or are there other process improvements to make the solder joint at the LED pad less than 10% per void? Thanks a lot.

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#82493

How to reduce solder joint voids of LED without using vacuum reflow? | 6 May, 2019

There are quite a few papers out there on the subject. Just enter "SMT void reduction" into google or other search engine and take your pick.

That said, slow ramp rates and paste volume reduction are a good place to start. Although I haven't tried it specifically to reduce voiding, I would think that a stencil thickness reduction might work better than an aperture reduction, assuming the actual volume reduction was the same.

There are also several "low void" pastes out there.

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#82500

How to reduce solder joint voids of LED without using vacuum reflow? | 7 May, 2019

I have personally never seen a reflow profile change reduce voids. We have invited "experts" in to demonstrate this claim. They were unable to.

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#82501

How to reduce solder joint voids of LED without using vacuum reflow? | 7 May, 2019

Probably just means you started out with an optimal profile.

I suspect that not everyone does. ;)

It seems like we did have some luck with profile adjustments in one instance with some QFN's with a large thermal pad. Like I said, though, the profile was basically trash to begin with.

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#82519

How to reduce solder joint voids of LED without using vacuum reflow? | 9 May, 2019

Hi, You can work on improving stencil design, having the perfect profile and other process improvements but it may be the paste itself letting you down. We have put a lot of work into developing our solder pastes to significantly reduce voiding. Your supplier should be able to help with choosing the correct paste for your application.

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SMTA-Rogers

#82650

How to reduce solder joint voids of LED without using vacuum reflow? | 27 May, 2019

Dear Steve,

Thanks for your feedback in our experience add solder paste volume is better for the voids reduce of LED type components.

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SMTA-Rogers

#82651

How to reduce solder joint voids of LED without using vacuum reflow? | 27 May, 2019

Dear Sr.Tech,

We tried to adjust the soak time and TAL time of reflow profile, but it doesn’t seem to help much.

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SMTA-Rogers

#82652

How to reduce solder joint voids of LED without using vacuum reflow? | 27 May, 2019

Dear Steve,

We already to do some DOE of reflow profile, but the optimized parameters are not help for the reduction of voids.

This message was posted via the Electronics Forum @ SMTASMTA

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SMTA-Rogers

#82653

How to reduce solder joint voids of LED without using vacuum reflow? | 27 May, 2019

Dear CW,

Yes, we also tested many different brands and models of solder paste, under the same stencil design and reflow profile the condition of the voids will have great difference.

This message was posted via the Electronics Forum @ SMTASMTA

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#82658

How to reduce solder joint voids of LED without using vacuum reflow? | 28 May, 2019

Solder paste flux is main contributor, Lead termination chemical-oxide by products and PCB Plating-Chemicals. Reflow profile would have very limited if not no impact really unless is way off.

Paste volume control and Stencil design plays a big part Paste Type-FLux plays a Part Device Pad layout and interconnect plays a part

Maybe get 20%-25% Voiding with above optimised is possible

Getting 10% or less doubt possible without Vacuum soldering. In EU at major OEMS in car biz this is all the rage Vacuum Soldering inside your convection oven in process. Pricy Machines but 2% or less can be reached. Major demand on void reduction is LED lighting as higher MTBF can be gained - less LED failure due to thermal stresses in LED device = better thermal management of LED Die in device.

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#82668

How to reduce solder joint voids of LED without using vacuum reflow? | 30 May, 2019

Contributors in order of importance:

1. PCB design - if you have large thermal pads, a grid of via holes should be created. Components with low profile will not let the gas to escape from the joint. The only way is going down.

2. Reduce paste volume for better performance

3. Stencil design apertures. There are techniques for reducing voiding based on stencil apertures

4. Low voiding paste - this has never been the best help. You should have a descent paste from a leading manufacturer.

5. Reflow profile - soak profile creates more voiding in general. Less heat improves voiding. You burn the flux and now oxidation will contribute to voiding. 6. Contamination and PCB storage - for places that don't control PCB and component storage and humidity. Oxidation and contamination will contribute to voiding big time.

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#82683

How to reduce solder joint voids of LED without using vacuum reflow? | 1 June, 2019

Increase paste volume and use ramp soak spike profiling. Reducing volume of paste often leads to entrapment. Good idea to know difference between voiding and dewetting due to contamination

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