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August 2007

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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 21 Aug 2007 16:16:22 -0500
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text/plain (266 lines)
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon
Sent: Tuesday, August 21, 2007 3:04 PM
To: [log in to unmask]
Subject: Re: [TN] [LF] Request for LF shrinkhole or hot tear failure data

Richard, where does 1-5 of your points reside in J-Std-001 and IPC-A-610? I read both and both C and D and do not see everything you are saying. I find the rework has to be documented but not that root cause has to be done each time a non-conformance or defect is found. Am I missing something? Just want to know, Thanks, Jon

 

 
Answer: See below. I have added the J-STD-001 paragraphs pertaining to the points.
  

 

 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, August 20, 2007 6:52 AM
To: [log in to unmask]
Subject: Re: [TN] [LF] Request for LF shrinkhole or hot tear failure data

 

Dewey,

Good to hear your plans for this. This is very encouraging.

The points in J-STD-001 and IPC-610 regarding that:

 

1. All rework shall be documented, no rework is to be performed that is not documented.

[Per sec. 12.1] 

2. Prior to reworking a defect, there must be some documented evidence that the root cause of the defect was found, or at least an attempt was made to determine the root cause (inspection, X-ray, etc.) or possible root cause(s).

[Per sec. 12.1 b]

3. There exists a formal means for providing the root cause of the defect back to the appropriate work center responsible for corrective action.

[Per sec. 11.3 Process control, especially sec. 11.3.1] Also refer to IPC 9191, a requirement flowed down through J-STD-001.

4. After rework is performed, it must be inspected, and verified acceptable through electrical re-test if the defect was found at electrical test originally.

[Per sec. 12.1] Passing electrical test is not actually required, as electrical testing is not a hard requirement. But if you had to rework something and electrical testing was part of the contract, would you not want to test after rework? That's pretty fundamental.

5. A system shall be in place to ensure that a second rework on the same component on the same serial no. assembly be reviewed prior to each subsequent rework at that particular component location.

[Sec. 1.5 "Class 3 shall develop and implement a documented process control system."] A process is not under control if the occurance of multiple reworks on the same component are not known. 

This last one is the basis of my request, that emphasis is placed on corrective action, not documentation of defects or trends. 


 

must be re-inforced.  

 

Now some of you think I am going too far, but let me explain why these requirements are important.

In too many places where I go to perform consulting work, I see a bonepile of circuit boards inside of a "hidden factory" that exists between the Inspection area, the Test area and the Rework area. Assemblies will fail electrical test and be debugged, a rework detail written up, and the assembly sent to a rework group. The rework is done, the assembly sent back into the bonepile at test, a different test technician on a different day re-tests the assembly without reviewing the history of the board. It may fail for the same thing (ie, an internal short or open or some other issue) and go into a vicious cycle of rework/test/rework before anyone realizes there is an issue with the board.

Too many places have no control over rework, they do not verify the rework fixes the problem and the board passes electrical testing, and the reliability of the board suffers for having been subjected to a number of reworks, unnecessarily.

 

-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)

Sent: Friday, August 17, 2007 3:40 PM

To: [log in to unmask]

Subject: Re: [TN] [LF] Request for LF shrinkhole or hot tear failure data

 

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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