Sheesh, just how much data do ya want? Shrinkage voids do NOT cause
reliability issues. Incoming:
- see page 873
- see page 17
Dave
Jack Crawford <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
08/14/2007 02:07 PM
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Subject
[TN] Request for LF shrinkhole or hot tear failure data
Revision E work has begun on IPC-A-610 and J-STD-001. A-610D addressed hot
tear/shrink hole in 5.2.11. I believe that the original intent was
specific to PTH connections, but as written, it can be applied to any LF
connection (SMT, PTH or terminal soldering).
I've gathered a few comments--mostly questions--about failure mechanisms
associated with hot tear. Several people claim evidence that hot tear
cracks continue to propagate in the connections.
Taking J001 and 610 literally, a fracture in a solder connection is a
failure. A common sense approach to the criteria would only have a
fracture to be a defect when it is in a critical area of a connection, but
that determination may require more knowledge and experience than the
typical user has.
610D provided for acceptance of hot tear/shrink holes only when the bottom
of the tear is visible or the tear/shrink hole does not contact the lead,
land or barrel wall. In response to a user's questions, Werner Engelmaier,
Engelmaier Associates, L.C., provided some information (copied below) that
suggests that even if the tear is at or propagates all the way to
conductor, lead or barrel, whether the bottom is visible or not, it isn't
likely to cause a failure of the connection.
My question to any of you is whether anyone can provide any evidence to
the 610 committee of connection failures that can unquestionably be tied
to a shrink hole or hot tear. Please don't reply standard improvement
comments to this forum for discussion--that's the function of the
committee and I may overlook the comment on the forum. Send them to me
[log in to unmask]
This is also a great time to send me any other comments you have against
610D, 001D, IPC-7711/21A or any other IPC document so the committees will
have them at MidWest Expo Committee Meetings
http://www.ipcmidwestshow.org/Std.aspx I'll get your comments to the
appropriate committee liaison.
Werner's comments to hot tear; some editing to remove personal
discussions.
From: [log in to unmask]
Sent: Friday, March 24, 2006 8:15 AM
Subject: Re: Fillet tearing
The described issues-pad lifting, fillet lifting, fillet tearing [also
called shrinkage fissures-are all caused by the same phenomenon. The
combination of larger delta-T from solidification to RT, the higher
strength of SAC-solders, faster cooling rates because of higher starting
temperatures creating more cooling rate differences, more complex
metallurgy, large differences in thermal mass, create stresses in the
solder fillets that will cause the 'weakest link' to give. Sometimes the
weakest link is the pad attachment to the resin matrix, in other cases the
interfacial strength between IMC layers and Cu pad, in in others the
solder volume itself.
Of course, none of these are pretty, but unfortunately, they are a
characteristic of the LF-soldering realities.
From a purely reliability point of view, none of these pose a mechanical
reliability problem, even long-term. These 'defects' do not pose a real
latent conditions in terms of loss of functionality.
I am more concerned with the possibility of corrosive damage, particularly
in the cases of pad lifting and fillet lifting, less so with fillet
tearing, because of the exposed Cu.
And I certainly would not make a differentiation between what is happening
on the termination side vs. the component side as 610D does. That makes
little reliability sense--if it is acceptable on one side, why not the
other? That looks to me like simply calling it 'bad,' because on the
tremination side you can see it and it is hidden on the component side.
As an example of a real reliability issue, I am much more concered with
accepting a 75% hole fill, because the stress concentration posed by the
partial fill can cause plated-through hole Cu barrel failure.
##### 2nd message
My comments regarding the effect on reliability rests on the general
situation, where through-hole leads exert virtually no loading on the SJs
during operation--there are, as almost always exceptions. I certainly have
seen PTH-leads that cyclically loaded pins/SJs to failure. The maximum
loading condition is typically along the leads or at most 45 °away from
the lead--thus, not really in line with the fractures.
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, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
#####
Jack Crawford, IOM
IPC Director Certification and Assembly Technology
[log in to unmask]
847-597-2893
FAX 847-615-5693
3000 Lakeside Drive, Suite 309 S
Bannockburn, IL, 60015
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