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'Cheap Boards'
1997\07\29@111215 by lilel

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One of you's guys wrote:
>If you're designing with PICS,  your board has to cost less than a
>meal at McDonald's

In my case, less than a Big Mac.  Some of our boards cost less than
$1.00 US.    A penny is one percent of the cost of these boards.
We are still designing through hole components on single sided copper
because it's the dirt cheapest system.  Or is it?

I've been examining the break even point between surface mount and
through hole parts.  We've been hanging onto through hole because,
till now, through hole resistors and other commodity parts have been
cheaper.  I think the break even point has about arrived, though.

Even in a surface mount design I'll be using some through hole
components - power resistors, relays, aluminum electrolytics,
vertical pots, etc.

One of the arguments against surface mount goes like this:  Surface
mount layouts require at least a double sided board.  Laying out
surface mount on a single sided board is a fool's errand because it
is difficult to jump across traces using a resistor.  You need that
second layer of copper in order to get the thing to route.  Two layer
boards are more expensive than single layer boards, ERGO surface
mount would have to be WAY cheaper than through hole to really be
cheaper.

So my question is this:  What to you folks think - is surface mount
cheaper than through hole?  Does surface mount require a two sided
board in order to route?


-- Lawrence Lile

1997\07\29@132452 by Ray Gardiner

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<snip>
>
>So my question is this:  What to you folks think - is surface mount
>cheaper than through hole?  Does surface mount require a two sided
>board in order to route?
>
>
There are some other things to consider as well as the points you
have mentioned.

1. SMT assembly costs are usually less than through hole.
2. SMT with smaller PCB size, packaging can be much less.

Whether or not you can route a single layer SMT board is the
same as for through hole. Only difference is your components
are now on the bottom of the board not the top :-)


Ray Gardiner  Technical Director DSP systems Pty. Ltd. spam_OUTrayTakeThisOuTspamdsp-systems.com
private email to:- .....rayKILLspamspam@spam@netspace.net.au          http://www.dsp-systems.com

1997\07\29@173721 by lilel

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> <snip>

> 1. SMT assembly costs are usually less than through hole.

This would be true in the US. We are having this stuff manufactured
in China.  Labor is, for all practical purposes, free.  It costs them
MORE to do surface mount because they have to have a skilled operator
running an expensive machine, whereas to solder through hole stuff
they put "free" laborers in charge of soldering irons.   A laborer
makes about $80 US a month, working 6 days a week at 10 hours a day.
Ugh.  And people grouse about Nike.

> 2. SMT with smaller PCB size, packaging can be much less.

In our application, the packaging is going to be an appliance which
will be the same size regardless of the board size.

Hmm.  So far it looks like through hole is winning....

1997\07\29@175049 by lilel

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> Whether or not you can route a single layer SMT board is the
> same as for through hole. Only difference is your components
> are now on the bottom of the board not the top :-)

I've routed some mixed smt/thru-hole  boards on single sided, going
nearly insane in the process.  Have you been successful at it?

1997\07\30@002410 by Ross McKenzie
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Lawrence,

FWIW, we have experienced bending of single sided PCBs with SMT parts and
subsequent stressing of solder joints and thin tracks. This doesn't appear
to be a problem with through hole techniques. You need to be careful to
balance the forces if mission critical applications are involved, especially
if your staff's attention to detail is paid for with peanuts.

Regards,

Ross McKenzie
Melbourne Australia

1997\07\30@014235 by tjaart

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Ray Gardiner wrote:
>
> <snip>
> >
> >So my question is this:  What to you folks think - is surface mount
> >cheaper than through hole?  Does surface mount require a two sided
> >board in order to route?
> >
> >
> There are some other things to consider as well as the points you
> have mentioned.
>
> 1. SMT assembly costs are usually less than through hole.
> 2. SMT with smaller PCB size, packaging can be much less.
>
> Whether or not you can route a single layer SMT board is the
> same as for through hole. Only difference is your components
> are now on the bottom of the board not the top :-)

'Tis true... Another thing : through-holes (sounds like an insult :
Hey, you through-hole! <G> ) don't work that well if you want to
place on both sides, whereas you can reflow on one side, and wave
solder on the other if you go SMT. The difference in price between
single-sided and double-side PCB is very small for us.

The price of 0805 prices have also gone down here. It should be the
same as 1206 pretty soon.

--
Friendly Regards

Tjaart van der Walt
tjaartspamKILLspamwasp.co.za
________________________________________________________
|        WASP International   http://wasp.co.za          |
|   R&D Engineer : GSM peripheral services development   |
|Vehicle tracking | Telemetry systems | GSM data transfer|
|Voice : +27-(0)11-622-8686  |  Fax : +27-(0)11-622-8973 |
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|________________________________________________________|

1997\07\30@102746 by lilel

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Ross was of the optinion that....

> FWIW, we have experienced bending of single sided PCBs with SMT
> parts and subsequent stressing of solder joints and thin tracks.
> This doesn't appear to be a problem with through hole techniques.
> You need to be careful to balance the forces if mission critical
> applications are involved, especially if your staff's attention to
> detail is paid for with peanuts.

OooH - hadn't considered physical stresses on the board.  My
predecessor designed a thru-hole board which bends 3/8" in response
to a lever that gets pressed down on it - I went ballistic when I
realized we had millions of these things in the field flexing away.
Adequate board support is much more critical in a surface mount
design.

-- Lawrence Lile

Download AutoCad blocks for electrical drafting at:
http://members.sockets.net/~llile/index.htm

1997\07\30@140724 by mike

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In message  <.....14405333201304KILLspamspam.....toastmaster.com> EraseMElilelspam_OUTspamTakeThisOuTtoastmaster.com writes:
> One of you's guys wrote:
> >If you're designing with PICS,  your board has to cost less than a
> >meal at McDonald's
>
[snips]
{Quote hidden}

Lawrence,

The answer to your question depends on the complexity of your circuit,
but I have some observations to make:

 - I find sm passives are easier to solder in place. There is no need
   to bend the leads, solder then crop. The board can stay on the
   bench an not be picked up and turned over etc. The sm ICs are more
   fiddly by hand, but if you ensure the pads are wider than that
   recommended it is easy enough.

   Just to clarify this, there are three phases in our projects in which
   we use PCBs:

   1) Prototype. The designer would solder the bits in.
   2) Pre-production. These would be in batches of 10 or 20. We have
      some outworkers who will do this for use. They prefer sm too.

   3) Full production. This is done by a contract company. They
      set up pick and place machines for the sm parts. Again, this
      is their preferred method.


 - I have laid out 2 projects now, 100 percent sm using only the
   component side of the PCB. There are no holes (I didn't need
   mounting holes), so the whole drilling process is removed with
   considerable cost savings. The circuits were small eg 16C71,
   max232 and associated caps, serial FRAM, 5 transistors, 3
   connectors and a bunch of Rs and Cs. The routing took some
   time, but I got there in the end.

 - This is subjective, but I think that sm looks the part. When I
   compare the sm boards to the old boards we used, there is no
   comparison - the sm boards look much better. Our customers get
   to see the boards from time to time, so it is important.


Regards,

Mike Watson

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