labsw/LOG: log of development

labsw/LOG

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+--- Thu 2011-09-01 ------------------------------------------------------------
+
+PCB milling #1:
+- setup:
+  - board is pertinax
+  - locally sourced "W.T." (Taiwan) mounting tape
+- measurements:
+  - board: 101.6 mm x 44.6 mm (nom. 102.0 mm x 50.0 mm)
+- defects found:
+  - drill broke on first hole, due to insufficient clearance found in
+    run #2. Second drill just cleared the board by sheer luck.
+  - drill/mill depth too shallow
+  - column cavities too wide
+- changes for next run:
+  - narrow column cavities from 8.4 mm to 8.0 mm (bad idea, see below)
+
+PCB milling #2;
+- changes made:
+  - board is FR4
+  - corrected depth
+- defects found:
+  - clearance insufficient (top copper damaged; endmill broke)
+- changes for next run:
+  - increase clearance by 1 mm
+  - future: include board thickness in gp2rml clearance calculation
+    (gp2rml calculates "clearance" from the highest point in the plot,
+   which for PCBs also happens to be the lowest point, and thus
+   includes the board itself and the vertical overshoot. 2 mm are
+   sufficient for 0.8 mm boards, but 1.6 mm boards need at least
+   0.8 mm more.)
+   
+PCB milling #3:
+- changes made:
+  - corrected clearance
+  - Tesa 5767 mounting tape
+- measurements:
+  - column cavity: ~7.6 mm x 10.3 mm (nom. 8.0 x 10.4 mm)
+  - board: 102.2 mm x 50.2 mm (nom. 102.0 mm x 50.0 mm)
+  - "narrow tongue": 9.1 mm (nom. 9.0 mm)
+  - "wide tongue": 14.1 mm (nom. 14.0 mm)
+- defects found:
+  - column cavities too narrow (also in design; need 8.4 mm)
+  - 100 mil header holes a little bit too small
+  - 200 mil header holes much too small
+  - rear edge touches wall
+  - front edge very close to buttons (not sure how close)
+- changes for next run:
+  - widen column cavities by 0.2 mm on each side
+  - compensate tool for 0.1 mm of board deflection on each side
+
+--- Fri 2011-09-02 ------------------------------------------------------------
+
+Layout printed on #3:
+- infrastructure:
+  - tried new approach of transferring both sides: instead of stapling
+    the two sheets, put adhesive tape around the edges. The result is
+    acceptable, but not as good as the work-intensive one side at a time
+    approach used for ben-wpan.
+  - battery pack for laminator control broke down mechanically. Replaced
+    with adapter for obscure 500 mil pack I had laying around.
+- problems found:
+  - "make it look like an accident" isn't such a good idea for the trace
+    connecting the relays to 5V. I was tempted to scratch off the toner,
+    thinking the pin had bled into the trace.
+  - annulus around DIP pins seems too small for 35 mil holes. The holes
+    are nominally only 0.5 mm, but that in turn may make them too small.
+- changes for next run:
+  - make 5V relay traces go clearly for the centers of the respective pins
+  - determine correct hole size for DIP
+
+--- Sat 2011-09-03 ------------------------------------------------------------
+
+Soldered #3:
+- problems found:
+  - DIP copper rings were too small for easy soldering, as expected
+  - cosmetic: screw-down headers (K1, K2) are very loose and end up
+    visibly angled
+  - cosmetic: vias between OUT opto-couplers are a bit close to the
+    sockets, making them almost disappear under them. Would be nicer if
+    they had more clearance.
+  - MCU and DIP sockets should have orientation markings on the copper
+    layer. In other news, Chip Quick is quite suitable for removing a
+    misplaced 32-LQFP.
+  - the footprints of the 1 W resistors (R7-R10) are way too short.
+    Placed 0805 instead.
+
+(next run)
+- changes made
+  - made 5V relay traces go clearly for the centers of the respective pins
+  - changed DIP hole size from 0.5 mm to 0.8 mm, hole-to-copper ratio from
+    2.5 to 2
+
+Pending:
+- widen column cavities by 0.2 mm on each side
+- consider pulling in front edge a little in buttons area
+- uncopper mounting holes (using "loop" as "if" in fped)
+- change mill nominal diameter from 35 mil to 26-27 mil
+- move vias between OUT opto-couplers 0.2 mm to the center
+- add orientation markings on copper layer for MCU and DIP sockets
+- verify 2512 footprint of 1 W resistors
+- add ground zones