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Stencil Bleed - Bridges and Solder Balls

Stencil Bleed - Bridges and Solder Balls

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I have noticed on a recent project, the QFN and SOP solder d... - Aug 14, 2023 by calebcSMT

First, this is the result of bad printer setup. Adjust knife... - Aug 14, 2023 by dima

Please elaborate, as I have already tried to rule out printe... - Aug 14, 2023 by calebcSMT

the implication being the soldermask is too thick, raising t... - Aug 14, 2023 by calebcSMT

Well gasketing yes, have you dine enough analysis to blame a... - Aug 14, 2023 by Spoiltforchoice

I'm actually currently in the process of discussing with ste... - Aug 14, 2023 by calebcSMT

Now you have to find the root cause, before you continue. Is... - Aug 14, 2023 by Evtimov

I'm curious what you use for PCB Support. Are you using a de... - Aug 23, 2023 by A Very Frazzled Man

Support bars, so essentially the board is sitting ontop of b... - Aug 23, 2023 by calebcSMT

Is there any outcome? ... - Aug 31, 2023 by MagyarT

calebcSMT

#89870

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

I have noticed on a recent project, the QFN and SOP solder deposits do not seem very uniform and have been leaving little balls, whiskers and icicles of solder paste coming from some pads which leads to bridges.

https://imgur.com/a/lqw5RF1 I have uploaded several photos illustrating the visual I am seeing. Does anyone have any insight the general cause and solution for something similar to this?

reply »

dima

#89871

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

First, this is the result of bad printer setup. Adjust knife pressure, PCB gap, separation speed, tooling, and stencil cleaning. Pay attention to the coating of contacts pad and height of solder mask of PCB.

reply »

calebcSMT

#89872

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

Please elaborate, as I have already tried to rule out printer setup. 0 contact of course, ive tried a multitude of pressures, separation speeds, cleaning frequency. Moreover, i use these settings for similar stencils and have absolutely no issue

i now lean towards improper reduction reducing gasketing

reply »

dima

#89873

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

Similar issues arose for me in cases where the contact pads of components were located below the solder mask level. Ordering a thinner stencil might potentially solve the problem.

reply »

calebcSMT

#89874

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

the implication being the soldermask is too thick, raising the top of the board higher than the pads themselves (eliminating gasketing)? Essentially, the board isn't perfectly planar would be the subject of cause it sounds like?

reply »

Spoiltforchoice

#89875

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

Well gasketing yes, have you dine enough analysis to blame aperture design- Maybe not?

Maybe whip out the gerber files for this PCB&stencil and compare the details with one you feel works well. Is there something different about their layout rules or apertures?

Some dirt or contamination on the tooling used on this board or elsewhere in your printer? Is the tooling appropriate for the panel in question? Is the blade an appropriate width for the panel.Is the stencil a good one and undamaged, are you sure you have coplanarity between the board and stencil?

reply »

calebcSMT

#89876

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

I'm actually currently in the process of discussing with stencil MFG regarding the apertures and reduction to see if perhaps it was not optimal for this fine pitch QFN, as just as you mentioned, we have similar products with similar QFNs that do not exhibit this issue.

reply »

Evtimov

#89877

Stencil Bleed - Bridges and Solder Balls | 14 August, 2023

Now you have to find the root cause, before you continue. Is it PCB design or printer setup? Or both contribute?

reply »

A Very Frazzled Man

#89923

Stencil Bleed - Bridges and Solder Balls | 23 August, 2023

I'm curious what you use for PCB Support. Are you using a dedicated support plate or are you using magnetic pins or some type of Grid-Lock system?

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calebcSMT