Electronics Forum | Wed Apr 27 12:26:49 EDT 2005 | jdumont
Square you say? Wouldnt this give less paste deposition than a circle and basically reduce the standoff height the same as making the pad bigger? Would using a type 4 paste for this size stencil aperture (.013") be a good idea? Thanks JD
Electronics Forum | Fri Dec 01 14:11:24 EST 2017 | kojotssss
EMIL, The first stencil was with 4 squares. then there was a worse percentage. Changed to the circles. Is better, but still not perfect. Stencil thickness did not change. I added 2 types of stencil openings. Pictures of watch:
Electronics Forum | Wed Feb 07 09:37:48 EST 2007 | billyd
Had the very same thing happen the first time we used the small QFNs. The aperture for the thermal pad in the center needs to be cut in a grid form, either squares (with around a 10 mil spacing between openings) or circles, like a BGA pattern. Too mu
Electronics Forum | Fri Jul 27 12:13:57 EDT 2007 | jdumont
We have issues with these also. They need to be flat to solder well. Reduce the square under the part for the heat sink and youll improve yields. That pad keeps the part lifted high while the other smaller joints reflow and partially attach. You can
Electronics Forum | Tue Sep 14 14:22:11 EDT 2010 | grahamcooper22
If the HASL was poor quality and very thin you would find this defect....but you would expect to see it on more pads also. Also, you'd expect to see your solder from your solder paste either dewetted on the pad or reflowed onto the BGA sphere making
Electronics Forum | Mon Jun 04 10:40:37 EDT 2012 | davef
I'm not aware of any such stipulation about witness [probe] marks for assembled boards, per se. Certainly, witness marks should not affect the intended performance of the assembly, you know, like damaging the solder connection or smudging solder mate
Electronics Forum | Mon May 14 14:51:36 EDT 2001 | Brian W.
Personally, I prefer the OSP. I get a flat surface to deposit paste on, resulting in more consistent solder paste volumes. With HASL, the amount of plating and the mounding affect the paste deposition. I have even had it affect the placement. The
Electronics Forum | Fri Dec 01 14:40:02 EST 2017 | emeto
Very interesting pictures. It shows paste height of 200um - which is at lest 6mil stencil deposit. That on the other hand posts another question. Can you measure the ground pad level in relation to the solder mask level with the SPI? I had assemblies
Electronics Forum | Fri Dec 22 16:04:26 EST 2006 | mika
Hi, This Not so easy as one wuold think. Has the thermal pad of yours vias? How many? What's the via's dia? What is the pcb thickness? If the the pcb has a "ground layer" connected (vias) to the pcb thermal pad, it could sometimes be a little bit tri
Electronics Forum | Wed Jan 16 15:22:29 EST 2002 | Terry Burnette
In his book titled "Manufacturing Techniques for Surface Mount Assemblies" author R.J. Klein Wassink describes the relationship between solder land dimensions, component lead coplanarity, board warpage, solder volumes, and solder paste flux wetting b
