> 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


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