2015-09-06

2015-09-13

Tried to use 3 um film on virtex die (waxed to SBT jig) and removed center before sides
Every previous lapping attempt I've done removed the edges first
Unusually large die: possibly wax accumulated in center causing bulge

Virtex die

Mostly decapped already by soaking in WFNA for a few days
Used piranha etch to clean up
Discovered remaining black epoxy/silicone doesn't quickly etch in piranha
Still have a pile of ones that require decap cleanup
Should have plenty for lapping R&D for a while
Decapping: https://twitter.com/johndmcmaster/status/642410779304570880
Bulk package removed via hotplate + pliers: https://twitter.com/johndmcmaster/status/642406536854138880
Original chips: https://twitter.com/johndmcmaster/status/641020243159052288
Sample:
- Thickness: 0.331 mm min, possibly as high as 0.335 mm
- WH: 19.9 x 20.4 mm
- Cut 20.5 x 20.5?

Lapping stencil

Idea: try to get closer to wafer lapping by not gluing chip down
Requires making a stencil to hold die in place
Use wax to affix stencil to fixture
Still using lapping films. Looking into getting condition rings + cast iron plate
All material: 0.01“ ⇒ 0.254 mm
- Should be < sample height but close to it
Kimwipe: 0.056 mm
- Must be < stencil thickness

Lapping jig stencil holder?

Should the stencil itself by held by a retention ring that slides up and down?
For now just lightly wax it on
- How much height will this add?
- Propose make slightly larger than sample holder and wax along top edge

Stencil cutting holder

Hold stencil in place on milling machine
Lapping surface 2” ⇒ 50.8 mm diameter
- 50.6 mm measured
Lapping jig cavity: 57.1 mm
Lapping stencil target diameter: 54 mm
- Add 1.5 mm to each side w/ 1.5 mm clearance
Support at least entire cavity size + 1/8“ endmill ⇒ 57.1 + 1/8 * 25.4 = 60.3 mm
Add some good clearance so I don't mill the jig: 5 mm each side ⇒ 70 mm total ID ⇒ 2.75”
0.5“ each side ⇒ 3.75” Al square stock
1.5“ from sherline t-slot to slot
- 10-32 (0.1900”) close fit ⇒ #9 drill (0.1960“)