wernermisc/labsw/LOG

--- 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