Steve,
I checked the source we use for our footprints and on the TSSOP 28
pin devices with the bottom tab, they suggest a pad the same size as the tab
and their common solder paste deposition of 0.006 - 0.008 inches. I haven't
used these particular TSSOP parts but I have used their footprints for years
without incident.
As for the reasoning, remember that the paste is made of balled
solder shapes typically, there is also a fair volume of flux and other
organics. The reflowed profile would be significantly less then the original
volume.
Sincerely,
Brad Velander.
Lead PCB Designer
Norsat International Inc.
Microwave Products
Tel (604) 292-9089 (direct line)
Fax (604) 292-9010
email: [EMAIL PROTECTED]
http://www.norsat.com
See us at Booth 323 at Satellite 2002 in Washington, DC March 6-8.
-----Original Message-----
From: Steve Baldwin [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 05, 2002 1:26 PM
To: Protel EDA Forum
Subject: [PEDA] TSSOP Power Pad
Does anyone have pointers to footprint guidelines for Power Pad
parts, particularly TSSOP (28 pin in this case).
If I put a pad down the same size as the powerpad and screen
solder onto it, I would expect the part to sit up on the meniscus
when the solder melts and I'd get poor/missed joints at the pins.
I would have expected to have a pad the same size as the power
pad but to only screen a tiny bit of solder on to it.
This is all conjecture and I didn't find anything useful with Google or
my usual PCB links.
Anyone know more about these things ?
Steve.
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