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Date: | Fri, 13 Jul 2012 16:15:23 -0400 |
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Hi Jack!
Thank-you for sharing this with the group! This is definitely going into my
reference folder!
I can imagine that Craig would be giving you a big high-five for this too!
Steve
-----Original Message-----
From: Jack Crawford
Sent: Friday, July 13, 2012 3:39 PM
To: [log in to unmask]
Subject: Re: [TN] Through hole barrel voids
About 13 years ago, before Revision C to J-STD-001 and IPC-A-610, the task
groups were struggling to resolve comments for hole fill requirements. The
leader of the IPC Assembly and Joining committee at that time was Jim
Maguire, then at Boeing and moved on to Intel. Jim pulled together a bunch
of pages (224 to be exact) about hole fill from publications and technical
presentations by industry experts. We scanned them to a pdf file way back
when so they are images only--not searchable text. They can be downloaded
from http://files.ipc.org/HoleFill-complete.zip
When referring to the hole fill criteria in J001 and 610, it's important to
remember that the criteria is intended as visual assessment--what are the
visible levels of solder within the hole. 75% fill means that there is no
more than 25% of visible barrel space (counting both top and bottom). It was
not intended and it is not appropriate to state that 75% fill requirement is
related to total volume of solder.
The topic of voids within the solder in the barrel--not visible without
x-ray or destructive analysis--has been discussed at IPC committee meetings.
More than one person has made the statement that voids within a solder
connection, including inside the solder in barrels, actually provides stress
release for the surrounding areas.
There is no current industry consensus on the maximum amount of voiding that
should be acceptable in solder mass within a barrel, in a BGA ball, or
within the solder between two flat surfaces (bottoms of BTC, gull wing
leads, chip components, etc.). Having followed these discussions for the 15
years I've been in IPC committee meetings, it's obvious that there are a lot
of opinions and even some good test data. Some of the Class 3 avionics and
weapon system manufacturers in particular want the conservative approach
(lower void levels) so it's been hard to move away from the 25% in BGA balls
and nothing has been established for other connections.
Regarding voids within PTH, I sometimes suggest to users that they find the
oldest functioning through-hole assembly they can find (some military
systems are 30-40 years old) and x-ray the assembly to see how much voiding
is in the holes. Find the connections with the largest void area in
connections that have not failed and measure. That isn't necessarily an
indicator of how much void will never fail, but I believe anyone that does
this will be surprised to see how many voids & the size of the voids that
have been in the products for decades without failure.
Jack Crawford
IPC Director Certification and Assembly Technology
IPC International Inc.
3000 Lakeside Dr. Suite 309S
Bannockburn, IL 60015
847-597-2893
Fax 847-615-5693
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www.ipc.org
www.ipc.org/status www.ipc.org/certification www.ipc.org/downloads
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