Electronics Forum | Mon Aug 14 01:29:49 EDT 2023 | calebcsmt
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 u
Electronics Forum | Tue Mar 03 02:39:56 EST 2015 | sarason
I would presume you reflow the top of the board first. Use tented vias. As you have worked out, vias have surface tension, which sucks the solder up the hole during reflow of the bottom of the board. Good luck! regards sarason
Electronics Forum | Tue Mar 03 03:11:57 EST 2015 | vb7007
Hi I also forgot to mention, top side is reflowed first at SMT. Tenting vias is good option. we are looking into it. Can you please also suggest any solution to avoid solder balls at bottom side in other places than vias. Thanks
Electronics Forum | Mon Sep 23 01:28:13 EDT 2019 | sssamw
Cannot understood your problem very clearly, please check IPC standard on QFN and its mfg process, also check the QFN supplier's recommendation, so can minimize the bridge.
Electronics Forum | Mon Aug 14 05:45:16 EDT 2023 | dimamalin
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.
Electronics Forum | Mon Aug 14 13:08:00 EDT 2023 | dimamalin
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.
Electronics Forum | Mon Aug 14 13:21:48 EDT 2023 | calebcsmt
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?
Electronics Forum | Mon Aug 14 13:51:37 EDT 2023 | calebcsmt
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
Electronics Forum | Mon Aug 14 14:17:19 EDT 2023 | emeto
Now you have to find the root cause, before you continue. Is it PCB design or printer setup? Or both contribute?
Electronics Forum | Wed Aug 23 17:22:39 EDT 2023 | markhoch
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?
