TECHNET Archives

November 1997

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Reply To:
TechNet Mail Forum.
Date:
Tue, 18 Nov 1997 18:39:11 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (51 lines)
Hi Max,
I have to disagree with Guenther somewhat.
There is no reason why J-lead solder joints should fail earlier than
gullwing-lead solder joints; most of the leads of the same pitch have very
similar lead stiffness. That is also the reason that fine pitch leads will
give you longer fatigue lives; they have significantly lower lead stiffness.

>- At high temperatures the solder is extremely easy deformable. Thus the
>stiffness of the lead doesn't matter much. Total relaxation will occur.
Not so. The low lead stiffness results in very low stress levels on the
solder joints and therefore almost never--particularly with the finer
pitches--does total stress relaxation occur. That is the reason why you get
longer lives for finwer pitches.

>- A good deal of the damage that occurs during thermal cycling in the solder
>joints of leaded components is not due to the global mismatch of component
and >PCB but due to the local mismatches of pin / PCB; pin /solder.
The local expansion mismatch is overstated in its importance for copper
leads; if it were dominant, finer pitch leads shoud not give longer
lives--but they clearly do as Guenter points out.

>J-leads cause more or less pure shear strain into the solder joints where
Gull >Wings cause shear strain in the solder gap and normal + shear strain in
the heel.
J-leads do not cause pure shear strain into the solder joints--just as
gullwing-lead solder joint start their cracks in the heel fillet, so do
J-lead solder joints.
A J-lead is much more like an inwards turne gullwing lead--that is the reason
why there is little difference in the way solder joints to gullwing- and
J-leads fail.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street                                 In December:                                    7
Jasmine Run Mendham, NJ  07945                                                              Ormond Beach, FL  32174  USA
Phone & Fax: 973-543-2747                         Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] 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.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
##############################################################


ATOM RSS1 RSS2