Minutes of the Tracker Meeting
Sandro reported that in
Sandro also reported on recent inspections of Tungsten tiles
as they were received at Plyform from the bead-blasting vendor in
Ben noted that the Plyform cleaning procedure (wiping with MEK) probably just removes part of the contamination and smears the rest uniformly over the surface of the tile.
Sandro asks for more information on the water break test for surface cleanliness. Ben recommended ASTM F22-02. Arthur will forward a copy of that to Sandro.
Sandro is writing a document to detail all the relevant Plyform procedures for the anomaly review team.
Encapsulation issue: the damage seen after thermal cycling was not caused by the glue needle. Instead, it is clear that the thermal stresses are delaminating the Nusil CV-2502 fill material away from both the Nusil 1142 dam and the silicon surface. The silicone glue then pulls the wires loose and kinks them. For some reason this only happens on the heavy trays. The only relevant difference that anybody could think of is the fact that the heavy trays bend slightly (100 um saggitta) when cooled or heated, due to the large asymmetry from one side to the other. On one heavy tray about 80% of the wire bonds broke during thermal cycling.
G&A would like to know the mechanical properties of the 3 Nusil adhesives: 1142, CV2500, and CV2502. Jeff will send that information (nominally in a wide range around room temperature the CTE is 320 ppm, and the modulus is 250 psi).
Several avenues are being explored to resolve this issue:
Tile grounding: Plyform proposed a solution that would ensure some electrical contact between the tungsten tiles and the tray structure. They would spread the adhesive on the tray as usual and then place by hand 8 long fibers into the glue, keeping the fibers well away from the tray edge. The tiles would then go on top. The 100-micron fibers would ensure electrical contact and would also help maintain the bondline thickness.
Jeff reported that the cable-fixation corner brackets will
arrive tomorrow and should ship to
Jerry said that there will be a meeting with Parlex tomorrow regarding the flex-circuit cable coupon failures. A large fraction of the “flight” cables are being rejected day by day due to incomplete connection between the via plating and the internal copper planes.
The review of the new pitch-adapter design will take place on Monday.
Albert reported that several non-flight MCMs were inspected for pitch-adapter cracks and will now go into a thermal chamber for 200 cycles -30C to +85C to see if the cracks open up or if new cracks are formed.
Jerry reported that the MCM boards in which bias shorts formed appear to be closely related in time during fabrication. Investigations are continuing. Tom Himel will direct the effort.