> On Sep 22, 2023, at 9:01 PM, Martin Bishop via cctalk <cctalk@classiccmp.org>
> wrote:
>
> ...
> Down to 0.5 mm pitch gull wing legs can be readily hand soldered by a
> wireman. Surface mount double sided PCBs can be hand assembled (by me), in
> small quantities, by restricting the components to 0603 and 0.65 mm pitch
> using an under board heater and hot air. The fine pitch stuff goes on first.
> OTOH a good wireman can hand solder 0402 components. So, don't back off
> completely from SMD. You "only" need: a quartz heater, a hot air wand, and a
> solder paste dispenser (you spit it on by hand). Note that surface tension
> squares everything up and moves the solder onto the pads; which need to be
> (hand assembly) oversize. NB this approach is for very low volume / zero
> budget / assemble tonight work; for serious boards / volumes you send the kit
> to the assembler.
I used to not mind sub-mm lead pitch; but my most recent bout with SMD (with a
TSSOP multi-RS232 transceiver) was enough trouble with my older hands that I'm
more hesitant now. Then again, the fact that I didn't make the footprint quite
wide enough undoubtedly didn't help. Leadless packages may actually be easier
-- no micro-legs to break off. Next time, maybe.
> BGAs are another story - dodge them; e.g. use
> https://digilent.com/shop/cmod-a7-35t-breadboardable-artix-7-fpga-module/ or
> similar to apply FPGAs in a 0.1" DIL form factor, at LVTTL levels. You could
> build an OmniBus interface with two of these, some bus interface chips 74LVC
> for Rx, something OD (and not too fast) for Tx, and a "host" processor.
There have been some good articles about assembling SMD boards (I think
including at least modest size BGA) using a toaster oven with a suitable heat
controller. John Wilson of Ersatz-11 fame made such a controller (an Arduino
daughterboard). For solder paste, some PCB shops make stencils quite cheaply,
or partner with a maker of those; OSH is one I remember. They might be the
classic stainless steel ones or a less expensive (and less but sufficiently
durable) material. I should try this one of these days.
paul
