[TriEmbed] a full custom biz card that runs Linux

[John Wettroth]

I think everyone experiments with SMT assembly to get to something that works.  I used a little Chinese clone pneumatic dispenser that pushed out paste through a blunt needle- its fine for small board if you can pull an airline into your lab.  The only designator is 983A, it must be a copy of something made by Hakko or Plato, etc.- I still use it but its only suited for really simple boards.  Hitting pads on a 300 pin BGA or a few hundred R's and C's is no fun.  Metal stencils are the way to go, they work so well- plastic does work but past can go under them pretty easily.  The only problem I have now is keeping solder paste from going bad and turning to concrete.  I have a little beer fridge in my lab and keep it in there which help.  I bring it up to room temp and if its too stiff, add a little Isopropyl- I don't go strictly by the expire dates- I can use it for 2 years or so though it might expire at 6 mos.  You can also put a little bit of liquid flux in it to liven it up.  It fails somewhat gracefully, you can do a test run and see if it will reflow without committing a bunch of boards.

I guess the original point of that post is the guy built a Linux box on a biz car- that's pretty cool.  I jumped to your stencil comment.

Regards,
John M. Wettroth
E: jwet at mindspring.com
M: (919) 349-9875 
H:  (984) 329-5420

-----Original Message-----
From: TriEmbed <triembed-bounces at triembed.org> On Behalf Of Pete soper via TriEmbed
Sent: Sunday, June 4, 2023 12:40 PM
To: triembed at triembed.org
Subject: Re: [TriEmbed] a full custom biz card that runs Linux

About 10 years ago OSH Stencils started out selling stencils made of 
kapton. The kapton came on rolls and there was curvature in the stencils 
such that 80% of the hassle of applying paste was holding the stencil 
down as flat as possible. For fine pitch parts it was a serious PITA. I 
was told kapton was used because it would cut cleanly. After Matt 
(owner) had shipped a zillion kapton stencils he could afford a serious 
laser cutter to offer stainless steel. For me this was a cause for major 
celebration. The time with the kapton was when stainless steel stencils 
from other sources were expensive. Now they are  cheap, as you noted 
John. A lot of the stencils I get from Matt are $10. A hobbyist might 
flinch at this cost, but IMO it's a small price to pay for the ability 
to actually assemble a board vs imagining that one can do it by manually 
putting paste to board. One can't actually manually put paste to board 
reliably for small parts. :-) Again, my focus is on small pitch parts as 
these have become a fact of life and avoiding them imposes a very heavy 
constraint on design. I'm preparing to make a flexible board for a 
sensor that has 10 pads around it's sides underneath and is 1.8x2.0mm 
overall. That takes a good stencil. :-)

A plastic that is dead flat to begin with and that doesn't go bonkers 
with a laser (i.e. that can be cut cleanly without the edges swelling) 
would IMO make for a cottage industry for somebody because they could 
beat the stainless steel prices and perhaps offer comparable quality 
results. But I'd have to see such a plastic stencil under my microscope 
to be convinced that it can actually compete with stainless steel. My 
'scope has a very good camera and I'd be happy to take pictures to share 
with the group so we could see what the apertures look like close up. 
("Aperture" is the 50 cent term for the mostly square corner holes in a 
stencil.)

Pete

On 6/4/23 08:09, John Wettroth via TriEmbed wrote:
> I've played with this with standard transparency film and a little 40w Chinese
> laser- takes a bit of tuning to get it all correct but works.  Stencils are
> really cheap when you order a board if you remember.
>
> Regards,
> John M. Wettroth
> E: jwet at mindspring.com
> M: (919) 349-9875
> H:  (984) 329-5420
>
> -----Original Message-----
> From: TriEmbed <triembed-bounces at triembed.org> On Behalf Of Pete soper via
> TriEmbed
> Sent: Saturday, June 3, 2023 1:51 PM
> To: Triangle Embedded Interest Group <triembed at triembed.org>
> Subject: [TriEmbed] a full custom biz card that runs Linux
>
> He made his solder stencil with a laser cutter and the BOM runs around $3.
>
> https://www.thirtythreeforty.net/posts/2019/12/my-business-card-runs-linux/
>
>
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