[TriEmbed] a full custom biz card that runs Linux

[Pete soper]

Wow, John. It never occurred to me to turn solder paste into "solder 
paint"!  Does that really work for you for .5mm centered QFNs?

Pete

On 6/4/23 14:01, John Wettroth wrote:
> 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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