Electronics Forum | Wed May 14 12:42:16 EDT 2008 | rgduval
Dave, Realized I didn't respond to one of your questions. We pasted and reflowed one board, with no components. This board exhibited extreme dewetting on all pads. The board was LF-HASL, and the paste was Qualitek (which we've used for approximat
Electronics Forum | Mon Apr 23 19:12:23 EDT 2001 | relensky
Thanks for the instructions. I was missing the reflow part... Omikron is the method our board house offers. We have been through the plating thickness problem and tin depletion conditions. Beyond those issues, I have been trying a few different n
Electronics Forum | Mon Apr 23 17:30:08 EDT 2001 | davef
Step 1: Print paste on the board, skip placement, reflow the board, check solderability. Step 2: Goto Step 1. White Tin Solderability: The most common reason for solderability issues with the white tin surface coating during multiple thermal excur
Electronics Forum | Tue May 13 08:26:29 EDT 2008 | davef
First, on your reflow temperature comment: The 183*C focus for reflow recipes for tin-lead solder is a falicy. If you held a recipe for tin-lead solder at 183*C peak, it would never reflow. Recipes for tin-lead solder need to be at liquidus plus 20*C
Electronics Forum | Tue May 13 20:48:10 EDT 2008 | davef
Rob On your thermal recipe: Above liquidous for nearly 2 minutes seems to be a scoush long. Not sure you're doing anything positive with things like that. On the article: * SMT Magazine, October, 2002, p24 'Q & A: BGA Dewetting' * "Q: Our manufactu
Electronics Forum | Mon May 24 05:53:24 EDT 2004 | johnwnz
Here's an interesting fact, some pastes just don't wet as well as others!.. there I've said it and now people will complain but that's life. Some pastes are formulated to run in air, some in N2, soem are specifically designed to be more aggressive fo
Electronics Forum | Thu Jul 05 13:47:10 EDT 2007 | arun2382
QFN assembled on a PCB indicates paramteric fails when tested. When the QFN on PCB is reflowed a second time, it recovers and passes testing. Visual, X-ray inspection revealed no anomalies. Cross-section images of solder joint revealed no anomalies (
Electronics Forum | Fri Aug 24 11:58:18 EDT 2018 | cupet
Hello davef, thank you for your reply. What do you think about the footprint for the diode on the first picture where the component is not assembled? There is good wetting on one pad of footprint and the other pad has bad wetting. This problem is not
Electronics Forum | Thu Jul 05 15:13:46 EDT 2007 | joeherz
We've seen non-functional QFNs cured by touching up the toe fillets. Especially with parts that are not plated on the edge/face where you get minimal/no wetting due to oxidation of bare copper. I'm not suggesting that you touch everything up but th
Electronics Forum | Fri Aug 24 08:49:54 EDT 2018 | davef
My first guess at the cause of your components skewing -- Termination pads on the board to not well match the the soldered terminals on the components, causing unbalanced wetting forces on the component terminations while the solder is molten.
