Document build process

Signed-off-by: Keith Packard <keithp@keithp.com>

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+                     Building MicroPeak Boards
+                           Keith Packard
+                             2013-01-11
+
+Here's the process I'm using to build MicroPeak boards. I build 15
+boards at a time.
+
+1. Apply paste to the boards.
+
+       1.1 Check the stencil alignment with a board. Somehow, it always
+           moves. Adjust and reaffix as necessary. The stencil is hinged on
+           the side of the board containing the ATtiny85 so that the tiny
+           ATtiny85 pads are the most carefully aligned.
+
+       1.2 Load a board.
+
+       1.3 Apply a bead of paste, on the far side of the ATtiny85 CPU. Spread
+           paste with the blade nearly parallel to the board. Then scrape
+           clean with the blade perpendicular to the board.
+
+       1.4 Clean the stencil every few boards to keep it from sticking to the
+           boards
+
+2. Load boards
+
+       2.1 Prep parts for five boards. I group them as they'll be installed
+           on the board. There are few enough that it's easy to tell where
+           every part goes.
+
+       2.2 Load parts on each board. I do them in this order:
+
+               1. 100k reset capacitor
+               2. 470 LED current limiting capacitor
+               3. Power switch
+               4. CPU
+               5. CPU bypass cap
+               6. LED
+               7. baro bypass cap
+               8. baro sensor
+               9. 4.7k SPI resistor
+
+2.3 After five boards are loaded, prep parts for the next five.
+
+3. Reflow boards
+
+       3.1 Group boards in a 3x5 array in the middle of the griddle
+
+       3.2 Preheat to 100C.
+
+       3.3 Turn off griddle power. Let it sit for 1 minute
+
+       3.4 Turn power back on and wait for all parts to reflow
+
+       3.5 Let it sit for 10 seconds after the last part reflows
+
+       3.6 Turn off power
+
+       3.7 Let parts cool on the griddle to below 100C
+
+4. Flash and self-test
+
+       4.1 Connect pogo-pin fixture to power supply and AVR programmer
+
+       4.2 Turn on power supply
+
+       4.3 Insert board, run 'make load' to flash. Note that a previously
+           flashed board will need 'make load-slow' to handle the 250kHz
+           clock speed.
+
+       4.4 Wait for the flashing to complete. Check for a single orange LED
+           flash which signals self test complete.
+
+5. Attach battery holders
+
+       5.1 Flow a small amount of solder onto the center conductor pad so
+           that it is raised high enough to hit the battery terminal.
+
+       5.2 Take the metal battery holder cage, align to the circuit board and
+           clamp the ATtiny85 end in a vise whose jaws are horizontal. This
+           end has enough board surface on the parts side to allow clamping,
+           especially if you align the bypass cap inside a gap in the vise
+           jaws.
+
+       5.3 Press down on the battery holder so that the exposed terminal
+           makes firm contact with the PCB pad. Solder in place.
+
+       5.4 Remove from vise.
+
+       5.5 With the vise jaws vertical again, place the board in the end of
+           the vise with the remaining battery holder terminal exposed.
+
+       5.6 Solder in place.
+
+       5.7 Load battery into plastic tray, install in battery holder
+
+6. System test
+
+       6.1 Power the board on. Make sure the LED blinks once
+
+       6.2 Insert into barometric testing chamber (35cc syringe)
+
+       6.3 Move plunger to 10cc mark. Insert plug
+
+       6.4 Wait for the altimeter to be ready for boost detect
+
+       6.5 Increase volume from 10cc to 20cc (halving pressure)
+
+       6.6 Make sure altimeter registers boost detect by blinking
+           quickly.
+
+       6.7 Wait 2 seconds, then decrease volume back to 10cc
+
+       6.8 Wait for altimeter to indicate landing by blinking out
+           maximum height
+
+       6.9 Verify that maximum height is approximately 5500m
+
+       6.10 Turn off power
+
+7. Package
+
+       7.1 Cut 1cm x 4cm piece of closed-cell foam
+
+       7.2 Insert foam into plastic bag
+
+       7.3 Push foam to bottom of bag with product card
+
+       7.4 Drop board into bag, move alongside foam
+
+       7.5 Push air out of bag and seal