Re: gEDA-user: anyone has had success with 0.2mm?

[Dave N6NZ <n6nz@xxxxxxxx>]

Randall Nortman wrote:
> On Mon, Dec 03, 2007 at 10:07:23AM -0800, Lope De Vega wrote:
>> I'm trying to build a circuit with a cp2102, which has
>> 0.5 mm between pins' center (actually 0.2mm between
>> pins). It is a qfn-28 package.
> 
> I have never played with toner transfer schemes,
Ditto for me...

 >  had them professionally printed,
> then I soldered the chips on by hand.  I have done it both with a
> toaster oven reflow process and with a plain old soldering iron.
Same here.  Toaster oven is great fun.

For hand soldering, round up the *smallest* tip you can for your 
soldering iron.  1/64 diameter, for instance. Flux is your friend.

> Having boards fabbed can be pretty cheap, especially if they're just
> one or two layers, and especially if you don't want soldermask.  It
> was cheap enough that I skipped right past trying to etch boards
> myself. 

Yes, having played in the soup many years ago, I'm perfectly happy not 
to do that part any more.

I've use APCircuits, and PCBExpress.com (division of SunStone, not to be 
confused with expresspcb.com...)  both with and without solder mask, and 
been very happy with the results.  A friend swears by Olimex, I've never 
tried them.

The cheapest I've seen for 1 or 2 copies of a board with mask and 
silkscreen is batchpcb.com, by the SparkFun guys.  I currently have 4 
designs sitting in "panelized" status, and I presume right now they are 
in the soup, or soon will be, someplace in China.  I've never tried them 
before -- I'll post a report when they come back.  Minimum order from 
batchpcb is one square inch -- your order costs $2.50 per square inch, 
plus $10 *order* set-up (not job set-up, so N designs in 1 order is 
still $10), plus shipping.  You can only order *with* two sided mask and 
two sided silk.

Anyway, at $2.50 per square inch, and a reasonable set-up charge, I 
can't get motivated to futz with toner transfer.  PCBExpress will do 6/6 
design rules in their prototype service, but if you back off to 8/8 
trace/space and 10 mil screen you will have lots of options for 
prototyping services.

Not to discourage you from trying toner transfer, of course :)  I have 
to say, though, that I'd try it out on something less aggressive than a 
fine pitch part for the first go.

-dave


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