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solder ball

Views: 1124

#84060

solder ball | 30 December, 2019

Hello All,

I am a SMT Engineer from Indonesia, I am facing the problem of soldering balls in only one IC location, in other areas there are none. solder ball defect almost 30%.

I have done several actions but failed to reduce the solder ball. 1. change preheat to be longer. 2. reduce the thickness of solder paste. (Metal mask thickness: 0.18mm). 3. change the "down speed" of the printer screen slower. 4. change the mount gap to be higher. 5. replace the IC with a shelf life of under 1 year.

additional info 1. ICs that occur solder ball, shelf life has passed 12 months from the bag seal date (March 2018) 2. The type of IC that occurs in a solder ball has a grounding pad on the bottom side (MSL level 3).

My question is whether the solder ball is caused by a shelf life of more than 1 year? or is there another reason? Does the IC have to be baking? what are the settings for baking?

Thank you very much and happy new year. Best regards agoes firmanto

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#84061

solder ball | 31 December, 2019

Do you have clear pictures show IC soldering and the solder ball? DO you have clear picture show the PCB pad?

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#84062

solder ball | 31 December, 2019

Dear Sir,

Thank you for your response. I show you the picture

Attachments:

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#84063

solder ball | 31 December, 2019

Attachments:

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#84064

solder ball | 31 December, 2019

From the picture, I cannot see clearly solder ball violate electrical clearance or cause a short, maybe it is.

What I can see is the solder paste has some misalignment although it doesn't printed in solder mask area, but actual position will reduce solder ball/solder short. And what's the IC pitch? Maybe 0.18 is too thick from the picture. If IC pitch is 0.5mm or 0.4mm, use 0.12 or 0.1mm stencil thickness is better. If a clear inspection for solder ball and IC lead to show wetting is good at that area, could tel us more possibility is related to solder printing, not IC itself.

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#84065

solder ball | 31 December, 2019

Yes, from the picture, it seems the gap between solder pad is very small, easy to have solder ball/solder bridge.

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#84068

solder ball | 31 December, 2019

This PCB model has been in production since 2018 and stopped production almost 1 year ago, now it has started production again and I found this problem. at the time of production in 2018 this problem did not occur. while the parameter settings do not change either the screen printer, mounter or reflow profile. Our spec for solder ball size is max: 0.2 mm. actually more than 0.2mm.

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SMTA-Davandran

#84071

solder ball | 31 December, 2019

You may try reduction on stencil aperture on the particular IC location. Reduction on width and extend outer length may help to minimise solder ball issue. However, please look into stencil foil thickness to meet AR.

This message was posted via the Electronics Forum @ SMTASMTA

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#84072

solder ball | 31 December, 2019

This one is easy. Go to 5mil stencil and reduce apertures in width. try to have 10mil aperture width and 10 mil distance in between. If you give us numbers we will be more precise.

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#84079

solder ball | 1 January, 2020

Solder ball attached on solder joint without violation minimum electrical clearance is acceptable. If your process parameter including stencil not changed, suggest you check if solder pasted being pushed out after IC placement, also check if solder joint wetting is good. Anyway paste on center of pad is better.

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#84086

solder ball | 2 January, 2020

Pretty large solder-ball. Looks like it may have come from the ground pad since it's so large, in which case I would reduce the print coverage on the middle/ground pad and see how it works for you.

You verified that these parts have the groundpad as shown on the PCB, correct? (Sounds like a stupid question, but you never know.)

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#84089

solder ball | 2 January, 2020

It is strange that you're having issues while using the same process parameters (including stencil) that worked successfully before. It doesn't guarantee that it's not one of those parameters changing in a manner that's not apparent, but it does suggest that you should be looking at anything else that could also have changed.

Are these PCB's from the same batch, or are they a new run?

Did you change anything about the paste (flux chemistry, powder size)?

Are your environmental parameters (room temperature and humidity) any different?

Edited to add that regardless of what changed, I'd *guess* that a new stencil layout for that part with reduced width apertures for the leads and a proper sectioning of the ground pad that gives you 30-40% volume reduction would take care of this issue regardless of what's going on elsewhere. The only reason I say *guess* is that you haven't shared the details of the component termination and stencil geometries.

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#84092

solder ball | 2 January, 2020

Hello Pak Agus,

Was there perhaps a change in solder paste? There has been confirmed occurrence in your case which happened in the work place I was before; all same parameter, equipment, material, and suddenly solder ball outbreak happened across all known models run. The condition persists for sometime until we decided to change solder paste into different brands, and the problem is solved completely.

While we can't be sure at that time is there a solder paste composition changes from manufacturer that was not informed to us, or something else, we don't know. All we know is all standard handling procedure including storage for solder paste was not changed.

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#84097

solder ball | 3 January, 2020

Sometimes might be internal change with personnel. Issue is actually there, but if no one questions it-it is not an issue. With 7mil stencil there is a good chance to have solder balls. So were they registered or were they fixed/cleaned?

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