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Solder balls

Views: 2618

#83731

Solder balls | 12 November, 2019

Hello Guys,

I'm new here. I am smt process engineer in new company located in Poland. I am responsible for whole smt line, so I have a lot of problems at the beginning :). I would like to ask about few things. The topic is solder balls. I produced some pcb's and I didn't had this problem before. After 2 weeks I took new pcb's, the same programs, the same stencil I discovered solder balls on the pcb. I am using 130 microns stencil, on the spi on the pads around I had solder balls height of the paste was 160 microns. What could be the reason of solder balls? Maybe I should change the squeeges for new one? Squeeges could be the reason of solder balls? Thanks for answer.

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#83732

Solder balls | 12 November, 2019

Some problem with screen printer process. You need to show photo of defect for understanding.

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#83741

Solder balls | 13 November, 2019

The answer is usually either too much paste or paste being deposited where it doesn't belong. In some instances the two are related. You don't say what kind of parts you're having problems with and that matters too.

I agree with the previous poster, though...pictures always help.

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#83760

Solder balls | 14 November, 2019

yes, first of all you need confirm if solder ball around solder pad has same location, if so then check squeege if has worn area or not at same location. If not, please check sodler paste itslf to see if dry a little, if so all paste could be a little obviously has ball seperated.

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#83763

Solder balls | 15 November, 2019

hi

i recommend following actions.

1) check the location where most solder ball is finding 2) verify the printer setting parameter if the problem is still persisting

please go below action

1. Stencil thickness should be 4 mil 2. Aperture opening of stencil should be 90% 3. C-cut or Ohm stencil design is recommended for all resistor and capacitor foot prints(0603,0805,2512) 4) reommanded electropolishing Stencil.

hope this will reduce your 95 % issues.

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#83768

Solder balls | 18 November, 2019

Did you reduce the apertures in the stencil? There can also be very large contact SMD pads. Can be the wrong the thickness of the stencil (thicker than need)

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#83769

Solder balls | 18 November, 2019

hi

initially, as per PCB design and gerber file of PCB we got 5 mil stencil, during process observed lot of solder balls (70-80%), then we decided to go for 4 mil stencil with c-cut. now the problem is reduced and still solderball exists which is acceptable to IPC standard.

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#83777

Solder balls | 19 November, 2019

Hello,

The first thing that you need to do is to make process mapping about this incident, so you can exactly determine all factors and observable changes happened during 2 weeks of timeline difference.

According to my experience, if all equipment (stencils, squeegee), machine parameter, reflow oven parameter are identical to last run, then you may point out on the solder paste itself. There are, according to experience, 2 kinds of contributing factors; the flux chemical composition, and how you handle your solder paste storage. Usually, when you have suddenly a solder ball outbreak, you may also see excessive flux after reflow in random but nearly homogeneous area among populated locations. On 1st factor, the flux composition changes is related to manufacturer. This need to be discussed with your supplier. 2nd factor related to storage which also contributed to flux property changes. Storage environment that is not as per recommended as per TDS of the solder paste in long exposure time can also become culprit of quality issue in the line (eg. solder ball).

Back to solder ball, not all solder ball conditions are considered defective. If you are running with no-clean process and encountered solder ball, you may want to check if the largest solder ball entrapped in flux residue and it is not violated the minimum electrical clearance.

Hopefully it's helping your troubleshooting effort.

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#83781

Solder balls | 20 November, 2019

We had a board we fought with for a while with solder balls. Checked everything, Stencil thickness at .004, reduced apertures, changed paste 3 times, changed profile 3 times. Finally changed board vendors. Went from HASL to Emersion Gold. Problem solved. Boards cost 1/2 of previous vendor and the quality was way better.

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