[Arm-netbook] EOMA68-A20 2.7.4 pre-production prototypes received and working

[Luke Kenneth Casson Leighton]

On Thu, Jun 15, 2017 at 3:16 PM, Bluey <bluey at smallfootprint.info> wrote:

> Is it an issue of gravity?  Perhaps it might be possible to
> apply the solder paste to the board in an upside
> down orientation (or even just at a high angle)?

the solder paste is applied with a stencil and (literally) a squeegee.
it sticks quite happily, and stays there even if the board's
upside-down.

 the problem is not the solder paste as it's applied, but when the
board's put into the oven.  that's where, when it reaches melting
temperature (240C or so?) it flows into the via holes... which are
something like 0.15mm wide (6 mil, aka 6 1/000ths of an inch).

 given that the pads themselves are only 7mil (0.2mm) wide, and only
about 25mil (1mm appx) long, there's far too little solder paste so it
just gets sucked down the hole.

 you cannot place the components upside-down on the PCB before they go
into the oven, if you do that they will simply fall off.

 l.