In a message dated 6/25/98 3:25:43 PM Pacific Daylight Time, Charles_Barker@I-
O.COM writes:
> I believe you have received very good info on the intrusive reflow and the
> MELF pad design (a "U" shaped pad). Some years ago I made a test board of
> different shapes, sizes, and spacings of pads for MELFs. You can see real
> quick, what works best. We wound up using a "U" shaped pad, but I don't
> recall the dimentions today.
>
> Good luck,
>
> Charlie Barker
> Sr. Manufacturing Engineer
> Input/Output, Inc.
> Stafford, Texas
> [log in to unmask]
> 281-552-3328 Voice
>
Hello All...
Charlie, I'm kinda' curious...yours is the second or third response I've
read saying that those "U" shaped pads work the best for MELF's. Maybe it's
just me, but every time I've had em' on boards I've built, they've not worked
any better than regular ol' square pads. In fact, sometimes the U-shaped pads
have caused a problem. What would happen is that the melf would wet only on
one side of the termination at opposing corners (yeah, I know melfs don't have
corners, but you know what I mean...) and the thing would be cock-eyed across
the pads...it would be 100% on the pads, but with a diagonal skew to it...and
when that happened, there was no fillet on one side of the termination because
there was no pad along that edge, as that's where the U-shaped cut-out
was...do ya' kinda' picture what I'm trying to explain?
I'm not trying to be argumentative here, but I really don't understand
what having a U-shaped cut-out on the pads where there's no solder paste
printed, have over a square pad where there IS some nice tacky solder paste
printed, to keep a melf from rolling around on ya'...
It's been quite a while ago, but I built this video switching board for a
company called Utah Scientific...it was a analog board and had a bunch of what
I guess were called channels on it. Basically, it was a pattern of SOT's,
resistors, capacitors, and melfs, that repeated itself a bunch of times across
the board...there must have been 1,200 components on that lil' bugger...it
would sit in a CP-4 for about 7-8 minutes, no kiddin'!
But out of the 1,200 components, there probably was 50-60 melfs and they had
square pads, and I never once had a problem with them rolling on me...
-Steve Gregory-
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