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July 2012

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
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
[log in to unmask]
www.ipc.org
www.ipc.org/status  www.ipc.org/certification  www.ipc.org/downloads


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