4 MB memory unibus/qbus card (was Qbus split I&D?)

[Jon Elson]

On 03/19/2015 03:59 PM, John Wilson wrote:
> Same experience here. Many fried boards until I tried 
> touching the (bare -- not sheathed) thermocouple to the 
> board (doesn't have to be in a PTH, although that might 
> stop it from occasionally twanging and sweeping components 
> off). I've only minimally tried BGAs (just liquid flux 
> w/no solder paste at all seemed to be the answer there) 
> but I've had fantastic luck with QFPs, SOICs, TSSOPs, and 
> and all kinds of SMT passive components. 
> www.oshstencils.com makes it just too easy. John Wilson D Bit 
Right, I've never tried the BGAs either.  I have done many 
thousands of SOIC and TSSOP parts, and a few thousand QFPs 
up to 128 pin 0.5mm pitch parts.  I've probably done over 
100K passives, generally 0805, but I have one board that is 
0603 that now works pretty well.  I do have a pick and place 
machine.

I make my own stencils with gear I used to use to make PC 
boards.  I get brass .003" shim stock and laminate it on 
both sides with dry film etch photoresist, just as if it was 
a PC board.  I have a laser photoplotter I made, and make 
the artwork for the solder stencil with that.  I make a 
normal and a mirror image, and glue them together on a light 
table, with a little spacer between to compensate for the 
shim stock thickness.  I just glue one edge and let the glue 
dry.  Slip the shim stock with resist between the artwork, 
expose both sides and develop and etch.  It took a while to 
get the whole process dialed in just right, but now it works 
quite well.  Part of the trick is to reduce the apertures to 
be smaller than the solder pads on the board.

Jon