[sdiy] SMT rationale? prototyping?

[James Patchell]

At 11:49 PM 7/18/2003 -0500, Paul Higgins wrote:
         Actually, stray inductance would be more close to it, but, the 
real reason for SMT is more related to manufacturing.  SMT parts are a lot 
easier to put onto a PC Board using automated machines than 
thruhole.  Getting a surface mount board built is a lot less expensive than 
a through hole board.

         Prototyping is a matter of personal taste and means.  I personally 
would not do any less than laying out a PC board that would be at least 
professionally made at a PC board shop.  These days you can prototype PC 
boards for $33 each, or less (well, really $100 per order..).  For that 
price, in my opinion, other options are just not cost effective....unless 
you just don't plain have the means.

>Forgive me for asking a (possibly) stupid question--I can't believe I've 
>never thought of this before!  Is the main rationale for the rise of SMT 
>parts--other than the increasing miniaturization of electronics in 
>general--the fact that stray capacitance that plagues through-hole parts 
>limits the frequency at which they can operate?  I just was poking around 
>inside my Mac, and it suddenly dawned on me (duhhhh...) that when you get 
>into clock speeds exceeding 2 GHz, you're gonna have some problems when 
>every pin looks like a few pF to ground.
>Furthermore, I remember reading something recently about how the PCB fab 
>people aren't terribly interested in letting engineers know what those 
>stray PCB capacitances really are.  (The author was discussing this in the 
>context of long PCB trace runs and their effect on audio).
>
>What do people recommend for prototyping with SMT?  I imagine that most 
>DIYers probably don't have robotics stuffing their boards.  :-)  I've seen 
>those SurfBoards which let you use SMT stuff with breadboards, not to 
>mention making the soldering of SMT parts to a board a bit easier.
>The conventional wisdom on this list seems to be that they're a rip-off.
>
>There is a TI/Burr-Brown part I use that is significantly cheaper in 
>SOIC-8 form than as a DIP-8.  We're talking several $$$ cheaper.  The 
>SOIC-8 package doesn't look too horribly intimidating; I think I can 
>handle this.  However, when I got my Atmel AVR starter kits recently, I 
>freaked out when I saw those TQFP-64 packages!
>
>What do people recommend for soldering equipment, etc?  I have a 
>temp-controlled solder station that I've been very happy with; I'm pretty 
>sure that I can get SMT tips for it.  Do I just need some liquid flux (and 
>a magnifier lamp and a truckload of patience)?  I've been soldering for 
>about 20 years, but I've never touched SMT until now.
>
>Also, what brand(s) of solder and flux do people prefer for SMT?
>
>Thanks to all.
>
>-PRH
>
>Paul R. Higgins
>email: higg0008 at tc.umn.edu