Hi Franklin,
We perform reliability testing by thermal cycle testing coupons and one
of my roles in the company is to analyze cracks in the PTH, dielectric
and fill if it is present. I microscopically examine hundreds of thermal
cycle induced PTH failures a year.
We frequently see cracks that propagate from a glass fiber, across the
copper of the PTH and through the PTH fill. Not in every case, but often
enough that it is not surprising.
We frequently find delamination in the dielectric is not continuous with
cracks in the barrel of the PTH. Most often delamination in the
dielectric protects the barrel of the PTH and the fill. Delamination
usually significantly extends thermal cycles to failure. Dielectric
delamination and extended cycles to failure is becoming a common
occurrence with advent of RoHS imposed lead-free assembly and rework.
On occasion delamination in the material will align with cracks in the
PTH and fill. Usually when that happens thermal cycles to failure are
significantly reduced.
I am of the opinion that it is the expansion of the dielectric that
causes cracks in copper and via fill.
Paul Reid
Program Coordinator
PWB Inc.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin D Asbell
Sent: Wednesday, March 19, 2008 6:33 PM
To: [log in to unmask]
Subject: Re: [TN] How much stress is needed?
Werner,
Would this also fracture the via fill material? I've seen fractured vias
before, caused by thermal expansion of the copper, but never one where
the via fill material is also fractured and yet the PCB is not affected
at all.
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Tuesday, March 18, 2008 9:45 PM
To: [log in to unmask]
Subject: Re: [TN] How much stress is needed?
Hi Franklin,
You describe a classic via barrel crack-comes from the thermal expansion
mismatch between the ED copper and the PCB resin in the z-direction
during the soldering processes [the hotter the worse-read lead-free]
[you should be taking my workshop on the subject at IPC EXPO/APEX on the
morniong of March 31.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
**************
Create a Home Theater Like the Pros. Watch the video on AOL Home.
(http://home.aol.com/diy/home-improvement-eric-stromer?video=15?ncid=aol
hom00030000000001)
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 15.0 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 15.0
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
-----------------------------------------------------
|
