Homebrew PCBs

Something mentioned on one of the boards, maybe old hat but hadn't 
seen it here in any of the thru hole discussions and it made a lot of 
sense..

  Use via pads and drill holes of just the right size, that will hold 
your SMT resistor.  Push it in and solder both sides, should be even a 
bit easier than dealing with wires.  SMT just a bit longer than the 
board is thick should make for a great via, with no bending wire ends 
etc, and held by the board so it's just push in and forget it till 
soldering.  Zero ohm resistors of the right length would make it a 
breeze, push in on a rubber mat with a small cupped tool and you should 
have just the right distance out each side of the board.  Heck should 
even work well for mounting a lot of non-zero SMT resistors too.

Alan

On Fri, 18 Nov 2005, Alan King wrote:

>   Something mentioned on one of the boards, maybe old hat but hadn't
> seen it here in any of the thru hole discussions and it made a lot of
> sense..
>
>   Use via pads and drill holes of just the right size, that will hold
> your SMT resistor.  Push it in and solder both sides, should be even a
> bit easier than dealing with wires.  SMT just a bit longer than the
> board is thick should make for a great via, with no bending wire ends
> etc, and held by the board so it's just push in and forget it till
> soldering.  Zero ohm resistors of the right length would make it a
> breeze, push in on a rubber mat with a small cupped tool and you should
> have just the right distance out each side of the board.  Heck should
> even work well for mounting a lot of non-zero SMT resistors too.

I've never heard of round SMT resistors...

Try this:

Obtain bare wire of the same size as the via holes and about half a foot
long.  Insert the end into a via hole.  Get a decent blob of solder on the
iron and still holding the wire, touch the pad/wire junction with the
blob.  Clip the wire and solder the backside.  There's no need to clip and
bend teeny-tiny pieces of wire.


-- 
David Griffith
dgriffi@...

On Fri, 18 Nov 2005 10:04:33 +0100, David Griffith <dgriffi@...>  
wrote:

> I've never heard of round SMT resistors...


It's called MELF (better mini-melf)
But square parts should fit as well.


I find the idea a bit crazy, it's certainly interesting, but i'm not sure  
i'd want to do that.

ST

----- Original Message ----- 

From: "David Griffith" <dgriffi@...>
> blob.  Clip the wire and solder the backside.  There's no need to clip and
> bend teeny-tiny pieces of wire.

Now he tells me. :) What a pain the arse *that* is. I just reworked a DS 
board to single side, and got it down to "only" 10 jumpers.

Speaking of vias, a few of them ended up under the chips. The SO packages 
barely make it, with a standoff height of 4 mils. I have one more SSOP 
package to glue on, due here tomorrow. I'm expecting trouble with that one. 
The spec says only 2 mils available underneath. Any advice? It's not just a 
via any more; it's a jumper now in a 24 mil hole on a SS board.

I think it's time for the heat gun; start over.

On Fri, 18 Nov 2005 11:05:53 +0100, Mike Young <mikewhy@...>  
wrote:

>
> Now he tells me.  What a pain the arse *that* is. I just reworked a DS
>
> board to single side, and got it down to "only" 10 jumpers.
>
>
> Speaking of vias, a few of them ended up under the chips. The SO packages
>
> barely make it, with a standoff height of 4 mils. I have one more SSOP
>
> package to glue on, due here tomorrow. I'm expecting trouble with that  
> one.
>
> The spec says only 2 mils available underneath. Any advice? It's not  
> just a
>
> via any more; it's a jumper now in a 24 mil hole on a SS board.
>
>
> I think it's time for the heat gun; start over.


my advice is:

avoid it! ;-)


if there's space, lift the trace, drill a larger hole where it was, bend  
it down into it and solder in there.


I've had to connect to the exposed pad to heatsink a flat component  
recently, and i drilled a larger hole and filled with solder. Surface  
tension is not your friend here, i think some stranded wire pieces stuck  
into the hole might have made it easier.

ST

Stefan Trethan wrote:

> I find the idea a bit crazy, it's certainly interesting, but i'm not sure  
> i'd want to do that.
> 

Curiously enough, that is almost exactly what went through my mind when 
I first came across the idea of re-melting laser toner onto copper as an 
etch resist :)

Pete

On Fri, 18 Nov 2005 15:24:09 +0100, Peter Harrison  
<peter_harrison@...> wrote:

>
>
>
> Curiously enough, that is almost exactly what went through my mind when
>
> I first came across the idea of re-melting laser toner onto copper as an
>
> etch resist
>
>
> Pete


Not really for me. TT, when it's done, leaves a pretty normal board, i had  
no worries there.
But having SMD resistors stuck through it does not leave something  
conventional. So there might be problems later on.
For example, thermal expansion might be something to think about, and not  
properly "seeing" the component another thing.

I'm not against it, but i'm very sceptical about it. also, the holes would  
need to be relatively big. I'd be more comfortable with wire vias, but  
then, i've gotten pretty good at avoiding them alltogether.

But i'm very curious to hear about results.

ST

David Griffith wrote:

>On Fri, 18 Nov 2005, Alan King wrote:
>
>  
>
>
>I've never heard of round SMT resistors...
>
>  
>
  Rectangular is as good or better.  Right size with right size hole and 
it'll insert a bit easier than an equally tight round one, and still 
have good grip.  Square pegs are very difficult to remove from round 
holes if they're a good fit.


>Try this:
>
>Obtain bare wire of the same size as the via holes and about half a foot
>long.  Insert the end into a via hole.  Get a decent blob of solder on the
>iron and still holding the wire, touch the pad/wire junction with the
>blob.  Clip the wire and solder the backside.  There's no need to clip and
>bend teeny-tiny pieces of wire.
>
>
>  
>
  That's not far off from general normal of what I do.  But with HQ 
dikes and assembly experience, it's easier and a bit faster for me to 
bend /cut each, then come back and touch all the silver spots with 
solder in a seperate pass.  Use silver plated wire wrap wire and they 
all stand out.

  As always, best and fastest method is just plain avoid the hell out of 
vias!  :)

Alan

Stefan Trethan wrote:

>
>Not really for me. TT, when it's done, leaves a pretty normal board, i had  
>no worries there.
>But having SMD resistors stuck through it does not leave something  
>conventional. So there might be problems later on.
>For example, thermal expansion might be something to think about, and not  
>properly "seeing" the component another thing.
>
>I'm not against it, but i'm very sceptical about it. also, the holes would  
>need to be relatively big. I'd be more comfortable with wire vias, but  
>then, i've gotten pretty good at avoiding them alltogether.
>
>But i'm very curious to hear about results.
>
>  
>


  With ceramic instead of copper, should have less expansion etc.  All 
zero ohm resistors would make it no real component to see anyway, just a 
nice little wire carrier that stays in the hole by itself before you 
solder..  But in with the original though was also that you could hide 
functional resistors this way, if you really worked at it you could make 
a board tougher to figure out..  Still, anyone looking at it with a 
meter should spot the non-zero trace resistances fast enough, even if it 
takes them a little to work out where the resistors are.

  Mainly mentioned it for the idea, I hardly ever use vias myself.  
Rectangular strip metal with indentions to make it snappable, and a 
press to press it and split the ends over to the sides, would be a dirt 
cheap via maker.  Wouldn't be circular like the other rivets so no 
through hole, but find metal strips already made and just sell 2 tools, 
one to perf the strip, and a press to cinch them in.  Still hardly worth 
doing, but 10 times less cost than the circular ones..

Alan

You know, a company i worked for, they pressed in 0.64mm headers into THP  
boards, as backplane, press fit, no soldering, and it worked well.
I reckon if one got roundabout that size square wire it would be good,  
since thinner wire mightn't take any pressure.
Maybe using extra long wirewrap headers is an option.

Anyway, i rarely use vias, i needn't worry.

ST

On Sat, 19 Nov 2005 01:01:38 +0100, Alan King <alan@...> wrote:

>
>
>   With ceramic instead of copper, should have less expansion etc.  All
>
> zero ohm resistors would make it no real component to see anyway, just a
>
> nice little wire carrier that stays in the hole by itself before you
>
> solder..  But in with the original though was also that you could hide
>
> functional resistors this way, if you really worked at it you could make
>
> a board tougher to figure out..  Still, anyone looking at it with a
>
> meter should spot the non-zero trace resistances fast enough, even if it
>
> takes them a little to work out where the resistors are.
>
>
>   Mainly mentioned it for the idea, I hardly ever use vias myself.
>
> Rectangular strip metal with indentions to make it snappable, and a
>
> press to press it and split the ends over to the sides, would be a dirt
>
> cheap via maker.  Wouldn't be circular like the other rivets so no
>
> through hole, but find metal strips already made and just sell 2 tools,
>
> one to perf the strip, and a press to cinch them in.  Still hardly worth
>
> doing, but 10 times less cost than the circular ones..
>
>
> Alan
>