Richard,

May not be an immediate solution for you, but a change to Ni/Au finish
at minimal (if any) cost penalty could provide a better way forward. We
spec Ni/Au in preference to HASL for anything with 25thou pitch or
smaller for the very reason/problem you state. HASL cannot give us the
level finish we need for fine pitch SMT.

Hope helps,

Clive ffitch
MBUK
Stevenage, England


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: 10 August 2000 00:55
To: <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a>
Cc: <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a>
Subject: [TN] QFP Pad Height Uniformity


                   *** WARNING ***

This mail has originated outside your organization,
either from an external partner or the Global Internet.
     Keep this in mind if you answer this message.


Hello all,

I hope I can relate what is happening here so all of you experts can
lead me
down a path! (Am I asking for it or what?)

25mil and 20 mil QFP's on a double sided PWB. We are seeing variances
in the
total height of the pad and resulting HASL finish. Specifically maybe
5-10
pads out of the 84 on the QFP exhibit an increase in HASL result in
that the
solder is mounded on top of the copper. The rest of the pads all are
flat in
nature with good HASL finish observed. We are being told that the
resultant
solder height is not controllable. Is this true? Is it unexpected to
see all
84 pads looking the same?

The situation came to light at the post printing process where a visual
inspection detected abnormal paste placement. We ended up with either
more
solder per pad (potential shorts) or less solder than normal (potential
reduced reflow) per pad. When I queried TechNet some time ago about
stencil
aperture sizes, the bulk of the results came back that apertures were
ordered at some percent smaller than the actual pad size. In the
neighborhood of 5-20% reduction.

If apertures are smaller than the pad size wont this add to problems of
uneven pad heights, assuming pad heights are not very well controlled?

As usual, Thanks in advance.

Richard Hamilton
Clemar Mfg. / Rain Bird
<a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a>

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a> with
following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information.
If you need assistance - contact Keach Sasamori at <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a> or
847-509-9700 ext.5315
##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a> with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at <a href="/scripts/wa.exe?LOGON=A3%3Dind0008%26L%3DTECHNET%26E%3D7bit%26P%3D651969%26B%3D--%26T%3Dtext%252Fplain%3B%2520charset%3DUS-ASCII%3B%2520name%3D%2522BDY.TXT%2522%26N%3DBDY.TXT" target="_parent" >[log in to unmask]</a> or
847-509-9700 ext.5315
##############################################################