Vendors always seem to advise using a thicker stencil for solder problems,
but never claim their product is unsuitable for use in designs with fine pitch
components, where a thinner stencil is required, in the spec sheet or
application notes.
Although I am confident your coplanarity problem stems from Motorola; I did
address this in a previous life. Found the problem with the PLCC program
parts used had coplanarity problems, everyone already guessed it, generated
in house during programming. As a young engineer assigned to gather
technical data to support the high profile 'quality issue' concerning
incoming parts, it was an experience to inform management that the problem
was internal and within an organization overseen by one of the more tenured
members of senior staff. Green and inexperienced I was, and took some
darts, but somehow managed to make no lasting enemies. GOOD
TIMES
Good Luck, the overprinting strategy is not likely to work if coplanarity
is the issue.
Brad Vanderhoof
AITI
----- Original Message -----
Sent: Monday, May 12, 2003 11:17 AM
Subject: [TN] Coplanarity of PLCC's
Technetters, I have been having a problem with a PLCC 68,
manufactured by Motorola, where about 1 out of 100 components have 1 corner
lead bent upwards creating no solder joint. It's usually pin 9 or 61.
I use a DEK 265 Infinity, laser cut 6 mil stencil, and no clean solder
paste. The feedback from Motorola is that the lead they measured from
one defect was within their coplanarity specification of .004". They
suggested using a 7 mil stencil, which I tried with no different result.
I also tried increasing the Z distance, to push the component into the
paste more, but I don't think there was much of an impact. It seems like
it would be very difficult to push this many leads further into the paste.
Theoretically, with a 7 mil paste deposit, and if the component went
half way down, then I would only have .0035" of allowance for coplanarity,
which would not suffice for the tolerance of this component, rig! ht?
My next plan is to
overprint the solder paste 20% longer than the pad (.08" x .025"), and use no
reduction of the width (I normally use 10% reduction), with the hope that the
reflowed solder would "bridge" the gap. I am hoping this will work, but
does anyone have another suggestion? Do you think its possible to push
the component further into the paste? A step stencil is impossible
because of the density, and there is nothing on the PCB with a finer pitch
than this component. Thanks in advance for your help.
Howard Watson
SMT Manufacturing
Engineer
---------------------------------------------------
Technet Mail
List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe,
send a message to [log in to unmask] with following text in the BODY (NOT the
subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery
of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To
receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]:
SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/html/forum.htm for additional information, or contact Keach
Sasamori at [log in to unmask] or 847-509-9700
ext.5315
-----------------------------------------------------
AMETEK/Dixson
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------