Trip to Teledyne on
Richard Gobin and Charlie Young
MIP-1 inspection was the original motivation for this visit to Teledyne. All recent MCM’s have been rejected due to excessive cracked traces; therefore, we focused on this problem instead. Three people from SLAC participated in the meeting:
Richard Gobin
Jerome Lepulu
Charlie Young
There were three people from Teledyne:
Brian Caplen
Jose Luis Saldana
Rhonda Santiago
Cracked Trace Problem
Teledyne re-started production on
Observations
Teledyne had seen large numbers of cracked traces in the past when the radius on the PWB was not well done. They inspected this group of bare boards and found “ridges” on the board as illustrated below. Richard and Charlie were not able to discern the features even with the aid of a microscope.
Teledyne then showed us examples after PA’s have been attached. The ring of light around the microscope’s lens becomes effectively two point sources in cross section. If the radiused part is uniform along the length, these point sources show up as straight lines.
The following two pictures are from a “good” MCM. It was rejected in any earlier run, but there were no problems with cracked traces. We can make out the last two digits of its serial numbers and will refer to it as S/N xx39. The pictures are from around U20 and U13 respectively. Note that the two bright lines are fairly straight. The traces fade away in the direction orthogonal to the bright lines due to poorer reflection. This fading is similar for all traces.
The next set of pictures is for S/N 2258, one of the 4 made
on
The next set of photographs is for S/N 2167, also made on
Known Process Changes
We are aware of only one change that might be related to this problem. The boards are radiused by Diamond Tools with a custom tool bit. Small irregularities were observed, and a step was added in early November. SLAC manually “deburred” the bare boards before shipping them to Teledyne. We did not control the radius while sanding, relying on the operator’s finger to conform to the board contour. The applied pressure depended on the operator. It was speculated this could have resulted in localized corners and flats, which led to traces cracking.
Other Possibilities
The PA’s may have come from a different production run than the ones used earlier, and may be more prone to cracking. The radius may have been put on incorrectly, either from a worn bit or from operational error.
Action Plan
Teledyne was convinced that the problem was with the “ridges”. We were willing to treat it as a non-exclusive working hypothesis. Here are some of the things to be pursued.
Other Items
Rework
Teledyne said most of the boards we sent back several months ago for rework were done. They were not shipped earlier because there was no Source Inspector to give OK. Jerome’s presence will take away that excuse. Teledyne promised a full accounting by middle of next week. We told them we expect to hear “everything has been shipped to SLAC”.
Production Schedule
The schedule that Teledyne provided last week is no longer valid. Production will re-start when the problem of 100% rejection is resolved. It is anticipated that the delivery schedule will slip by that amount.
PA Pull Test
As reported before, the pull tests have been done. Brian has not finished analysis of the data.
Encapsulation Test
We will use some of the 18 rejected boards to see if replacing silicone based Kapton tape with acrylic based tape improves the bond. Teledyne will attach dead dies, and wire bond 4 boards. [Having dies means we don’t need to modify the flow to compensate for the volume. Wire bonds may be useful during QC.] They will be cleaned in the usual way and then encapsulated. Rhonda will contact Dave Rich for permission to carry this out under the $10K testing contract. They will be subjected to the usual handling at SLAC, including temperature cycling and burn-in. Quality of encapsulation will then be evaluated with sonogram, sectioning, and other techniques.
Cover Tests
The first test was successful. We will continue testing as a back-up solution to encapsulation. SLAC will get new covers made, using an acceptable material and with more precise dimensions. Teledyne has no action until the new covers are available.
Vacuum Bagging
When shipping from Teledyne to SLAC and from SLAC to INFN, the MCM’s are vacuum bagged. We are not sure why this is done. We do not know why this should not be done with the current design. On the other hand, if we were to use covers instead of encapsulation, vacuum bagging may deflect the covers and damage wire bonds.
Clean Room
There was a leak in the roof near our production area. Water was being collected in a bucket.
We observed no production activity in the clean room during this visit; there was not a single operator there. The construction area has grown. It is separated from the production area by a sheet of plastic. We observed workers going through the production area in street clothes.
Teledyne said these people were involved with construction and/or repair of the roof, and it was impractical to make them suit up. We were examining rejected parts, and no potentially accepted parts were exposed. 12/29/04 was scheduled as a clean-up day to scrub the clean room in preparation for production on 1/3/05. It was not obvious that the construction and repair would be done by then.
Appendix I – Serial numbers.
Date |
Serial Number |
Fixture |
Trace Problem |
|
||
MCM |
PA |
>8 |
power |
|
||
12/20/2004 |
958 |
2134 |
1 |
x |
x |
|
|
2346 |
2138 |
2 |
x |
x |
|
|
2248 |
2137 |
3 |
x |
x |
|
|
2402 |
2131 |
4 |
x |
x |
|
|
2017 |
2147 |
3 |
N/A |
N/A |
|
|
2397 |
2146 |
1 |
N/A |
N/A |
|
12/22/2004 |
2175 |
2148 |
1 |
x |
|
|
|
1364 |
2132 |
2 |
x |
|
|
|
2270 |
2112 |
3 |
x |
x |
|
|
2130 |
2159 |
4 |
x |
x |
|
|
2057 |
2160 |
3 |
x |
x |
|
|
2140 |
2173 |
4 |
x |
x |
|
|
2167 |
2172 |
2 |
x |
x |
|
|
2258 |
2171 |
1 |
x |
|
|
12/28/2004 |
2097 |
2187 |
1 |
N/A |
N/A |
|
|
2011 |
2185 |
2 |
N/A |
N/A |
|
|
2283 |
2182 |
3 |
N/A |
N/A |
|
|
2053 |
2196 |
4 |
N/A |
N/A |
100%
reject |
9/7/2004 |
11292 |
674 |
1 |
|
|
|
|
11293 |
677 |
2 |
|
|
|
|
11296 |
681 |
3 |
|
|
|
|
11298 |
707 |
4 |
|
|
|
9/8/2004 |
861 |
373 |
1 |
|
|
|
|
11186 |
368 |
2 |
|
|
|
|
11234 |
388 |
3 |
|
|
|
|
11295 |
423 |
4 |
|
|
|
|
11201 |
334 |
1 |
|
|
|
|
11203 |
335 |
2 |
|
|
|
|
11227 |
336 |
3 |
x |
x |
|
|
11231 |
338 |
4 |
|
|
|
9/9/2004 |
11188 |
346 |
1 |
|
|
|
|
11228 |
342 |
2 |
|
x |
|
|
11229 |
343 |
3 |
|
|
|
|
11233 |
348 |
4 |
|
|
|
9/13/2004 |
869 |
574 |
1 |
|
|
|
|
913 |
572 |
2 |
|
|
|
|
12239 |
576 |
3 |
|
|
|
|
11237 |
573 |
4 |
|
|
|
|
989 |
879 |
2 |
x |
|
|
|
992 |
863 |
3 |
|
|
|
|
11000 |
843 |
1 |
|
|
|
|
11352 |
884 |
4 |
|
|
|
9/14/2004 |
11275 |
690 |
1 |
|
|
|
|
11239 |
697 |
2 |
x |
|
|
|
11272 |
735 |
3 |
|
x |
|
|
11284 |
748 |
4 |
x |
|
|
9/16/2004 |
11243 |
788 |
1 |
|
|
|
|
11248 |
798 |
2 |
|
|
|
|
11266 |
809 |
3 |
|
|
|
|
11353 |
816 |
4 |
|
|
|
9/17/2004 |
11178 |
210 |
1 |
x |
x |
|
|
11213 |
239 |
2 |
|
|
|
|
11297 |
259 |
3 |
x |
|
|
|
11300 |
631 |
4 |
x |
x |
|
9/20/2004 |
11269 |
320 |
1 |
|
x |
|
|
11235 |
321 |
2 |
|
|
|
|
11242 |
324 |
3 |
|
x |
|
|
499 |
325 |
4 |
|
|
|
|
11003 |
326 |
1 |
|
|
|
|
11199 |
327 |
2 |
x |
|
|
|
11037 |
328 |
3 |
|
x |
|
|
11195 |
329 |
4 |
|
|
|
9/22/2004 |
995 |
337 |
1 |
|
|
|
|
11019 |
322 |
2 |
|
|
|
|
11093 |
716 |
3 |
|
|
|
9/27/2004 |
764 |
672 |
1 |
|
|
|
|
11440 |
671 |
2 |
x |
|
29%
reject |