[sdiy] moving to SMD/SMT

[Tim Parkhurst]

> -----Original Message-----
> From: Tony Clark [mailto:clark at andrews.edu]
> Sent: Tuesday, October 12, 2004 7:55 PM
> To: john mahoney
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] moving to SMD/SMT
> 
> 
>    Well the first and most obvious thing to keep in mind is that SMD
> parts exist only ONE side of the PCB!  That means that if you use a
> double-sided board, traces on the bottom side do eventually have to make
> it to the top before they'll connect to anything!

*****************************************
 
Well, actually you can do double sided SMT boards. I see it all the time.
I've even seen SMT parts attached to the bottom side of a board with a small
dot of epoxy and then soldered by running them 'face down' through a wave
solder machine! Double-sided boards are a little tricky to do with
conventional solder paste/reflow oven techniques, but again, I have seen it
done. As far as DIY, I would just be careful about placing a part that will
require lots of heat and solder on the opposite side of small or sensitive
parts. Other than that, you'll need vias or 'jumpers' to connect traces on
one side to the other (same as you would with through-hole parts), but then
just flip the board over and solder away.

BTW, I've also soldered boards with a hot-air gun. I was at a customer site
once (used to work for a company that made SMT Pick and Place machines),
when their IR reflow oven went belly up. We had already screened the solder
paste and placed parts on about a dozen boards, so I had two guys put on
some gloves and they held the boards while I went to work with the air gun.
It actually worked VERY well, and you could see exactly when the solder
started to flow (made it easy to verify that I was heating the board evenly,
and that I didn't heat it more than necessary). As long as you keep the air
gun moving and heat the board evenly, it was very easy to manage. Of course,
approach the board from a slight distance and work your way in, and make
sure the parts are set properly into the solder paste so you don't blow any
of them off the board (come in from the top, rather than at a steep angle).
I would actually try this before I would do the toaster oven thing. One
advantage these methods have over hand soldering is that there is actually
LESS chance of damaging components from thermal shock because you are
heating the entire board and the components at the same time. A hand held
iron concentrates the heat in a small spot, so you get a large thermal
variation over even a small component. That being said, working with solder
paste is a PITA and you can learn to safely solder SMT parts by hand with
just a little practice. 

Just my US$0.02


Tim (hot-air gun) Servo

"Epoxy always has the right 'thread'" - Toby Paddock

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.776 / Virus Database: 523 - Release Date: 10/12/2004
 



***************************************************************************
This message is confidential.  The information contained in
this e-mail message is intended only for confidential use of the
recipient(s) named above. If the reader of this message is not the intended
recipient or an agent responsible for delivering it to the intended
recipient, you are hereby notified that you have received this document in
error and that any review, dissemination, distribution, or copying of this
message is strictly prohibited.  If you have received this communication in
error, please notify us immediately by e-mail, and delete the original
message.
***************************************************************************