Justin,
Has your design department been using this pad geometry for some time? The
pad geometry is not very forgiving of mis-placed parts in the Y axis. It
only allows for a nominal solder fillet of 0.037mm (itty-bitty") for a part
at min length, and no external fillet for part at max length. The Y
dimension being close to the dimension of the part termination does not
inspire confidence either. The fact that the X dimension is wider than the
part is probably the reason for skewing (depending on whether it's
rectangular or oval). The pulling off of one pad but soldered to the other
could mean that one joint is reflowing sooner than the other, part
mis-placed, not enough solder paste, part near maximum length, thick part,
*pad geometry*. Could be other things.
Suggest that you create a "dummy" board with various pad geometries and
part orientations, and find out which one works best for your application.
Might start with IPC / vendor recommendations and then work from there to
create a manufacturable design standard. We have been using the IPC
standards for years in high shock & vibration environments with good
results.
Have to agree with Shahed, why put vias in between 0603 pads? If the vias
are so small why stop there, why not buried vias or buried vias in pad?
Are the designs that compact?
Roger M. Stoops, C.I.D., PCB Designer
Trimble
Engineering and Construction Division
5475 Kellenburger Rd.
Dayton, OH 45424-1099 USA
Ph: +01 937.233.8921 or +01 937.233.4574 ext 288
Fax: +01 937.233.7511
"Braime,
Justin" To: [log in to unmask]
<jbraime@RACALI cc:
NST.CO.UK> Subject: [TN] 0603 land pattern debate
Sent by:
TechNet
<[log in to unmask]
G>
08/31/01 05:13
AM
Please respond
to "TechNet
E-Mail Forum."
Hi all,
I have had some problems with a recent build with 0603 capacitors. The
problem was that they were either very skewed or were soldered to one pad
only (pulled off the other). The land pattern for the 0603 cap on this
board
was (I thought) fairly questionable. Using the IPC-SM-782 terminology, the
current design is:
X = 1.27 (0.05")
Y = 0.508 (0.02")
G = 1.016 (0.04")
Our design dept's justification for this design is based on being able to
put a via between the pads, but to my mind the G value is too borderline
for
consistent results. Also, I think the X value is a little on the high side
-
hence the skewing.
I'm now trying to convince the design guys to adopt the IPC guidelines - at
least the recommended G value anyway.
I'd appreciate anybody else's thoughts on this!
Incidentally, we placed 0402s on the same board with very few problems :)
Thanks
Justin Braime
Senior Production Engineer
Thales Instruments Ltd.
480 Bath Road
Slough
SL1 6BE
Tel: 01628 604455 x 392
Fax: 01628 662017
Email: [log in to unmask]
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