On 30 Jun, 18:12, "numeric" wrote:
Hi,

I would like to build a PCB board with fine pitch (LQFP32) and very small
surface mount parts (1206 and smaller) parts. The board is a simple 24 bit
A/D and D/A converter with a full speed (12 Mbs) USB2 interface; although I
would prefer the USB2 high speed interface (480 Mbs). The temptation is too
hard to resist using today's microprocessors such as SiLabs C8051F350
(basically an 8051 cpu). I know that a commercial 4 layer PCB with a solder
mask would probably work for homebrew construction; but the board cost is
high.

So what is the chance of a double sided PCB without solder mask working with
very small parts? The process I would use in either case would be:

1. Place solder paste on all pads. Typically, when heated the solder will
vacate between pins and will suck up, like a magnet, under the SMD pin.

2. Place glue under parts that will possible move when the board is handled.

3. Heat the PCB in a toaster oven until soldered. Manually follow the heat
up and cool down time curves for type of solder paste used.

Comments/suggestions are appreciated.

I don't have any problems making PCBs at home for 0.5 mm lead spacing
QFPs, or soldering them. by hand (drag soldering).

Leon