I noticed that you are soldering at 500F. That sacrifices reliability on
SMT, especially for chip caps.
Also, soldering at lower temperatures can reduce shorts.
I've used the old Hollis air knives (of different design revisions). You
will get mixed results on the knife, its an art to get it set up right. At
the shop that had them, we eventually threw them in the trash on most
machines. We regularly changed products prior to tweaking in the air knife.
If you do purchase an air knife, get the design with the heater at the
blades. Heaters 3 feet from the orifice tend to provide uneven
temperatures. Set it up so that all solder joints reflow for at least 1
second with gentle pressure. The residual rosin will act as the flux.
Raising the pressure can blow the solder out of barrels (like HASL) and
blow your shorts all over the PCB surface, resulting in splashes,
solderballs and webbing.
Be sure to take the liquidus time into account when doing your wave
profile. With a 500F wave, you may be exceeding component specs on the QFP
and chip caps when you add in additional liquidus time with an air knife.
ARIC PARR
Sr. Manufacturing Engineer
Eaton Corp
1400 S. Livernois
P. O. Box 5020
Rochester Hills, Mi 48308-5020
[log in to unmask]
248 608 7780
Fax: 248 656 2242
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG, on 4/19/99 6:35 PM:
To: Aric Parr@01635@Lectron_RH,
EatonWHQ@CorpMail@WHQCleveOH[C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG],
Dean Jones@01635@Lectron_RH, Luis Arevalo@Automotive Eng@AACOCarolStrmIL
TN'ers:
We're getting a handful of bridges at wave solder on a few designs. We've
tried A, B, and C, but they continue to show up consistently on some styles
of connector behind chip components, and on trailing leads of flatpacks.
The machines is a fairly new Electrovert with convection preheat, Lambda
wave, and chip wave. We're using Sn63 at 500F with RMA 25%.
We're looking at a hot air knife retrofit, which would be turned off on
everything but problem boards. We've had a demo, with mixed results.
Good:
bridges were much improved, and no insufficients. Not-So: some frosty
looking joints, which we expected, but also a lot of solder balls and
splashes.
We've heard that setup can be touchy, and we didn't expect to optimize on a
two board sample, but we're not sure what we can conclude here.
Unfortunately, the demo was not apples-to-apples - it was performed on an
inerted machine with an A-type wave, and we're not sure if the splashing
and
balls could be attributable to the increased surface tension.
Anyone out there have good things to say about their hot air knife?
Joe Kane
Lockheed Martin Control Systems
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