Jim,
What are the pads and gap dimensions?
We usually see tombstoning on wrong/marginal foot print design no matter
what is the trace width.
It does of course contribute to the imbalance but with a correct design
it does not have any influence.
Mickey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of James Verrette
Sent: Tuesday, May 16, 2006 11:53 PM
To: [log in to unmask]
Subject: Re: [TN] 0402 Experience and Pitfalls
Hi Kerry,
How much of an improvement in tombstoning did you see with ENIG vs. HASL
when the traces going to the parts were balanced?
I have always heard of trace imbalance as the major reason for
tombstoning, but I guess the solder volume imbalance makes sense too.
If the HASL can range in thickness from .1 mil to 1.5 mils (number I've
seen somewhere correct me if I'm wrong), that can create a significant
difference is solder volume with a 5 to 6 mil stencil. Typically, how
much difference in solder volume is required to tombstone an 0402 part?
I guess that would depend on part height, mass, etc.
-Jim
________________________________
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, May 12, 2006 10:09 AM
To: TechNet E-Mail Forum; James Verrette
Subject: Re: [TN] 0402 Experience and Pitfalls
Hi Jim,
I saw that when I used HASL originally, I could not guarentee that I
would have the same deposition of solder on each Pad during the HASL
process. This left me with 2 pads that had different deposition of
solder on them. This imbalance caused me to see more tombstoning of the
0402 devices during relflow. When I switched to ENIG (bad topic to
mention today), which has a more planar surface, the tombstoning was
minimized.
Let me know if you need more info. I ran a pretty good DOE on 0402's
back in 98. We also looked at the weight of traces going into the pads.
Both factors will affect tombstoning. The RF boards we were running
were 3.5" x 3.5 " with 250 (0402"s) on both side.
Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
50 Rosemont Road
Westwood, MA 02090-2306
(T) 781-467-5468
James Verrette <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/12/2006 09:06 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
James Verrette <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] 0402 Experience and Pitfalls
Kerry,
Please elaborate on your recommendation, Do not use HASL finish.
What specific problems occur with 0402s on HASL finished PCBs and what
aspect of the HASL finish causes them? Typically HASL is avoided for
things like BGAs fine pitch large pin count packages because of the
relatively poor uniformity compared to other finishes, but I would not
think that this is a concern for a two pin device.
Jim Verrette
Electrical Engineer
------------------------------
Date: Wed, 10 May 2006 09:11:26 -0400
From: Kerry McMullen <[log in to unmask]>
Subject: Re: 0402 Experience and Pitfalls
Hi Ryan,
Approach them the way you would a 0603 DOE. The biggest thing I saw that
keeps tombstoning to a minimum is to keep a large area gap between the
pads, and also try to balance the trace widths that come into the pads.
I use a .006 thk stencil with rectangular pads and 1:1 aperature
openings.
Also, do not use HASL finish.
I stay away from glue.
I could go on, but lets see what everyone else says.
Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
50 Rosemont Road
Westwood, MA 02090-2306
(T) 781-467-5468
---------------------------------------------------
Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
________________________________________________________________________
_____
Scanned by Sanmina-SCI eShield
________________________________________________________________________
_____
_____________________________________________________________________________
Scanned by Sanmina-SCI eShield _____________________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
