SMT By Hand

Hi,
I’m just starting to build some boards specifically using MCU's
and other components, some of the components I wish to use only come in
fine pitch SMT packages. I have looked into reflow and how the
components are normally attached to boards using solder past (solder
cream) and then put though a oven that controls the heating up and
reflow and cool down process carefully. I noticed that most components
im looking at have a heat up to 150˚ C at 1 to 3 degrees a second to
ensure not to damage the component. Now as far as I can see I only have
2 options to using such components:
1.) build a small reflow oven that is computer controlled and can be
programmed based on the components I’m using, this option is not
expensive but is extremely time consuming.
2.) pay for a shop to fabricate the boards (which is expensive when
dealing with small quantities).

I was wondering if it’s possible to place such components using a hot
air pencil, but these will obviously heat the component up very
quickly, based on the reflow specs I assume this would damage the
components?

Any other fast and not so expensive options?

Thanks for your time.

 

[Lionel]

On 7 Jan 2007 00:37:36 -0800, profofeecs@hotmail.co.uk wrote:

I was wondering if it’s possible to place such components using a hot
air pencil, but these will obviously heat the component up very
quickly, based on the reflow specs I assume this would damage the
components?

Any other fast and not so expensive options?

Well, I hand-fix boards with big SMDs (eg; 64 pin QIPs) every now &
then, & as long as the PCB is solder-masked, & you take your time,
it's not anywhere near as hard as it looks. I manage okay with a
standard Weller bench station, a fine tip, & a magnifying headset.
The easiest method to solder in a new part is to freshly tin the
lands, hold the chip in place with a wooden stick (half a skewer works
well), & tack in a pin at two opposite corners. You can then use the
skewer & tiny taps of the iron to get the chip placement 100% right,
then solder the rest of the legs, working your way towards the corners
you tack-soldered in. The really important thing is to use very quick
touches of the iron at all times, & to always use the surface tension
of the solder to 'draw' the bead away from the body of the chip.
I'm not explaining it very well, I'm afraid, this one of those
techniques that're much easier to demonstrate than to explain.

 

[Brewer720]

On Jan 7, 3:37 am, profofe...@hotmail.co.uk wrote:

Hi,
    I’m just starting to build some boards specifically using MCU's
and other components, some of the components I wish to use only come in
fine pitch SMT packages. I have looked into reflow and how the
components are normally attached to boards using solder past (solder
cream) and then put though a oven that controls the heating up and
reflow and cool down process carefully. I noticed that most components
im looking at have a heat up to 150˚ C at 1 to 3 degrees a second to
ensure not to damage the component. Now as far as I can see I only have
2 options to using such components:
1.) build a small reflow oven that is computer controlled and can be
programmed based on the components I’m using, this option is not
expensive but is extremely time consuming.
2.) pay for a shop to fabricate the boards (which is expensive when
dealing with small quantities).

I was wondering if it’s possible to place such components using a hot
air pencil, but these will obviously heat the component up very
quickly, based on the reflow specs I assume this would damage the
components?

Any other fast and not so expensive options?

Thanks for your time.

I also have done a great deal of rework involving surface mount devices
(large devices with VERY fine pitch) and the previous directions are
good. The only thing that I could add would be to suggest that you get
a flux pen and apply a good liberal coating of flux to the pads and the
pins before you start soldering. The flux will make the solder bead
better and greatly reduce the number of shorts that you get between
pins. Then you can use a flux cleaner when you are done to clean the
excess flux off of the board.

This is very much within the realm of the home hobbyist if you use a
good iron, magnification of some kind, good lighting, and take your
time.

 

[ErnieWin16]

At my last job before we got the SMT equipment up and running we soldered
SMT parts by hand. For resistors, put some solder on one pad, keep molten,
and with tweezers slide it into place. Then solder the other side. With
chips, anchor one or two corner pins with solder, then do the rest, and
reflow the first. I even had to solder the real fine pitch ones using only
the very tip of a 10W iron. I'm not sure what the actual pin size was, but
maybe about 2 pixels wide if held up to the screen. Soldering SMT by hand
is tricky, but you just gotta go slow.



profofeecs@hotmail.co.uk wrote in message
<1168159056.592471.62750@51g2000cwl.googlegroups.com>...
Hi,
I’m just starting to build some boards specifically using MCU's
and other components, some of the components I wish to use only come in
fine pitch SMT packages. I have looked into reflow and how the
components are normally attached to boards using solder past (solder
cream) and then put though a oven that controls the heating up and
reflow and cool down process carefully. I noticed that most components
im looking at have a heat up to 150° C at 1 to 3 degrees a second to
ensure not to damage the component. Now as far as I can see I only have
2 options to using such components:
1.) build a small reflow oven that is computer controlled and can be
programmed based on the components I’m using, this option is not
expensive but is extremely time consuming.
2.) pay for a shop to fabricate the boards (which is expensive when
dealing with small quantities).

I was wondering if it’s possible to place such components using a hot
air pencil, but these will obviously heat the component up very
quickly, based on the reflow specs I assume this would damage the
components?

Any other fast and not so expensive options?

Thanks for your time.