Electronics Forum | Fri Aug 13 13:50:53 EDT 1999 | Brian Wycoff
| | | | | | Hello | | | | | | | | | | | | Having a problem with bridging on 20mil pitch qfp, only on the lead groups where squeegee goes over width of apertures. Using MPM sp-200 semi-auto, chem-etch stencil, 9-10mil width opening | | | | | | 100 du
Electronics Forum | Tue Apr 11 16:42:56 EDT 2000 | Chad Notebaert
I�m thinking �Poor intermatallic� It could be a few things. Lets start at the beginning. -Is your paste a 63/37 mixture? -Have you monitored you screen printing, Verify Solder deposition, Are you getting enough paste? -You say the solder looks like i
Electronics Forum | Wed Jul 27 09:58:05 EDT 2011 | davef
Pressure printing systems Conventional stencil printing techniques have fundamental limitations as regards paste handling: The volume of paste available for printing is limited, so frequent replenishment is necessary Paste is difficult to c
Electronics Forum | Thu Apr 15 17:06:08 EDT 2004 | russ
What are your temps at the locations that you are having trouble with. We cannot tell anything by the zone settings of an oven. We need max temp, how long above liquidous etc.. a lot of times this symptom is due to too long of a soak at too high o
Electronics Forum | Fri Apr 23 12:47:29 EDT 2004 | barry
I have increased my peak to 220, and Flow is better, but it still not quite a good fillet all around. The solder tends to kinda "bunchup" at the toe of the lead. If part is Pb free, would this affect adhesion and or flow?
Electronics Forum | Thu Apr 22 12:27:47 EDT 2004 | barry
I placed thermo's at 2 of the problem devices. Soak (time 150 to 180) 100 sec. Time above 180 =80 secs with 208 deg. peak. The solder appeared to flow at these pads, but little to no adhesion to the joint.Total time in oven was 5 min. All other joint
Electronics Forum | Fri Apr 23 13:31:20 EDT 2004 | russ
The toes of leaded devices are problematic in fillet formation. A lot of the time they have the copper from the lead exposed so it becomes oxidized and won't readily take solder. Normally this is of no concern if the heel and side fillets are forme
Electronics Forum | Sat Apr 17 17:08:22 EDT 2004 | finepitch
Russ has a hint by saying "too long of a soak at too high of a temp or being in reflow for too long/hot". I think the board should stay in the oven for 3-4 minutes, spending 60-90 seconds of which during reflow. in order to stay in the oven for 3 m
Electronics Forum | Tue Sep 30 14:06:04 EDT 2008 | realchunks
What pitch? You can go 5 mil or even 6 mil stencils depending on your screen printer. Also what do you consider "less solder"? What defect are you having. Remember on a QFP you use the heel filet to determine proper solder joint - not the toe.
Electronics Forum | Thu Oct 02 08:26:41 EDT 2008 | rway
We had similar issues until we went to a 6 mil stencil thickness.
winsouce.jpg)
