AVR-Chat

Hi there,

I wonder if solder paste is easier for soldering
atmega128 on a board. I tried solder wire and
the result is not too good and bridges formed
frequently. It could be that I am using wire
that is too thick. And my inexperience on soldering
SMT parts definitely did not help at all. :)

If solder paste will do wonders, any recommended
brand. I can use just regular iron with it, right?
No hot air blower required?

thanks
thomas

Last time I stuck down SMT parts I used flux (flux is your friend) on 
the pads first, put a tiny bit of solder on them flux 'em again (a 
flux pen is good).

Then tacked down the corners of the chip after making ABSOLUTELY SURE 
it was lined up properly (because you're not pulling it back off if 
you screw up).  Check it MANY TIMES to make sure it's turned/aligned 
properly.

Then solder down the rest of the pins.  Clean up any excess solder 
with a desoldering braid.  Last thing to do is to check each 
connection.  Actually this is a lot easier than you'd think.  Just 
run a pin from your meter over the pins slowly.  As it slips over the 
pin it will make a noise.  Loose pins make a dull sound you'll 
recognize right away.

Hope that helps a bit...might want to check into SMT soldering 
guides.  There are many available but I'm too lazy to check



--- In AVR-Chat@yahoogroups.com, "nangkon" <nangkon@y...> wrote:

> Hi there,
> 
> I wonder if solder paste is easier for soldering
> atmega128 on a board. I tried solder wire and
> the result is not too good and bridges formed
> frequently. It could be that I am using wire
> that is too thick. And my inexperience on soldering
> SMT parts definitely did not help at all. :)
> 
> If solder paste will do wonders, any recommended
> brand. I can use just regular iron with it, right?
> No hot air blower required?
> 
> thanks
> thomas

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

From: "nangkon" <nangkon@yahoo.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, December 23, 2003 3:14 PM
Subject: [AVR-Chat] solder paste vs solder wire


> Hi there,
> 
> I wonder if solder paste is easier for soldering
> atmega128 on a board. I tried solder wire and
> the result is not too good and bridges formed
> frequently. It could be that I am using wire
> that is too thick. And my inexperience on soldering
> SMT parts definitely did not help at all. :)
> 
> If solder paste will do wonders, any recommended
> brand. I can use just regular iron with it, right?
> No hot air blower required?
> 
> thanks
> thomas

Tried awg 28 solder (28 guage wire width) ?
I got myself some kester  RMA FLUX 28AWG 63/37 
comes in 2.2 kg(1LB) pack. (not cheap but worth it).

Any similar sized (fine)solder should be fine.

http://www.bdmicro.com/smt/
http://www.avrfreaks.net/Freaks/Articles/ColinSMD/intro.php

What iron tip size are you using ?

And what method are you using ?



No don't use a normal iron with solder paste.
You will end up with a big mess.

Alex

> I wonder if solder paste is easier for soldering
> atmega128 on a board. I tried solder wire and
> the result is not too good and bridges formed
> frequently. It could be that I am using wire
> that is too thick. And my inexperience on soldering
> SMT parts definitely did not help at all. :)
> 
> If solder paste will do wonders, any recommended
> brand. I can use just regular iron with it, right?
> No hot air blower required?

Solder paste is always easier for small components, as it
contains quite a lot of flux, is gooey and will therefore help 
hold the components into place. This removes the need
of an extra hand when soldering. 
The problem is the normally rather low "open time" of the 
paste (< 1 week), and the price.

I always use solder paste, I've found that Kester is the 
best for manual work, Multicore the worst. Kester paste
will (in a syringe) hold for several months, no need to keep
it in the fridge.

For resistors and other passives in 0603, 0805 sizes, a VERY
small dot of paste on the pad is enough. For integrated circuits,
I simply put a thin string of paste over all the pads. 
This works perfectly, I've assembled hundreds of  PCB's this 
way, without any problems.
I normally use hot air, but this will work as well with a fine
tipped soldering iron.
Don't worry about any solder bridges, simply remove these
afterwards with Soder Wick.

But, as with ANY other method, it takes some training.

I've tried ALL the methods, different pastes, solder wires, 
solder in the corner, in the middle, not at all. After all these
boards, I've found the way that _I_ believe is the best.

/Jesper

There is a good app note on soldering at the avrfreaks.net site.

Al 

-----Original Message-----
From: nangkon [mailto:nangkon@yahoo.com] 
Sent: Monday, December 22, 2003 8:14 PM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] solder paste vs solder wire

Hi there,

I wonder if solder paste is easier for soldering
atmega128 on a board. I tried solder wire and the result is not too good and
bridges formed frequently. It could be that I am using wire that is too
thick. And my inexperience on soldering SMT parts definitely did not help at
all. :)

If solder paste will do wonders, any recommended brand. I can use just
regular iron with it, right?
No hot air blower required?

thanks
thomas



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Hi Thomas,

On Tue, Dec 23, 2003 at 04:14:06AM -0000, nangkon wrote:

> I wonder if solder paste is easier for soldering
> atmega128 on a board. I tried solder wire and
> the result is not too good and bridges formed
> frequently. It could be that I am using wire
> that is too thick. And my inexperience on soldering
> SMT parts definitely did not help at all. :)
> 
> If solder paste will do wonders, any recommended
> brand. I can use just regular iron with it, right?
> No hot air blower required?

Solder diameter makes a big difference.  Too large a diameter and you
end up applying too much.  I found that even a 0.03 inch diameter
solder is too big to reliably solder the ATmega128 by hand.  I use a
0.015 inch diameter flux core solder: Digikey part # KE1203-ND.  Use a
smallish iron tip, my iron tip is a general purpose chisel tip.  You
can see photos and a tutorial on my site here:

	http://www.bdmicro.com/smt/

Set your iron rather hot - I use 630 F.  Use the iron to heat the pin
near the knee of the pin.  Bring in the solder near the foot of the
pin.  It should melt instantly - you only need a small amount of
solder, perhaps 1 or 2 mm worth.

If you cause a bridge, a bit of desoldering braid and/or some flux
will correct it.  However, with a little practice you should be able
to solder without making any bridges.  I can't remember the last time
I made a bridge doing ATmega128's, and I solder them a lot :-)

Also, while my eyesight is very good, I still use a 5x magnifying
visor which helps a great deal.

I've used solder paste, but only when using a surface mount oven.  I
usually only do that when I need to make up 10 or more boards.  In
that case, a stencil helps a lot to apply the solder.  The stencil is
a stainless steel template that is an exact cut-out of all your solder
pads.  You position that over your board, then squeegy the solder
paste over the stencil and lift it off.  It leaves just the right
amount of solder on each pad.  Place your parts, pop it into the oven,
bake until done :-) Afterward there are usually 2 or 3 bridges to
clean up.  I got my stencil from these guys:

	http://www.stencilsunlimited.com/

I was very happy with their quality and service.

-Brian
-- 
Brian Dean, bsd@bdmicro.com
BDMICRO - Maker of the MAVRIC ATmega128 Dev Board
http://www.bdmicro.com/