Jack,
I was going to let this go, but we just had some more discussions with Richard and Denny on rework versus repair.
I have stayed out of J-STD-001 and IPC-A-610 meetings to concentrate on IPC-A-600, IPC-6012, IPC-6011, IPC-6013, IPC-2221, IPC-4101, IPC-SM-840 and the Blue Ribbon Committees to make sure we have a bullet-proof(lead or otherwise) printed board so no matter if even you or Doug gets near it with any soldering equipment, it will survive.
The concern I have and have had is the merging of IPC-7711 and IPC-7721. With the IPC-7711 there was an expectation that the assembly when reworked would meet the acceptance criteria of J-STD-001 and/or IPC-A-610.
In the changes to both in the new revisions, process indicators will be revisited and the requirement to document rework. There will need to be accountability for all the potential non-conformances; the documentation and ultimate disposition of those non-conformances; the plotting of the metrics on SPC charts; the review and analysis of RTY; CPK benchmarks and Configuration Management Plans all the way back to the serial number of the bare printed board and the associated coupon on which the lot acceptance was based.
Requirements forIPC-7721 shall be AABUS.
Dewey
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Jack Crawford
Sent: Tuesday, August 14, 2007 12:07 PM
To: [log in to unmask]
Subject: [LF] 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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