small soldering job

[[email protected]]

Hello
Can someone recommend a soldering/manufacturing service that will do
a small soldering job for me. Just 2 ICS: one TSOP 44 pin and a TQFP
144 pins. Well there is no solder mask on the PCB, so I think they have
to be soldered manually instead of using wave soldering.

Will

 

[Pooh Bear]

Hello
Can someone recommend a soldering/manufacturing service that will do
a small soldering job for me. Just 2 ICS: one TSOP 44 pin and a TQFP
144 pins. Well there is no solder mask on the PCB, so I think they have
to be soldered manually instead of using wave soldering.

If it's a prototype I'd hand solder it anyway.

It's not tricky when you've had some practice.

Don't bother with solder paste ( it ' goes off ' fast anyway ) - just use
ultra thin cored solder ( I think mine is 0.8mm ) and a very fine tip. Pin
down the corners of each chip carefully to locate it, then attack the other
pins.

You *will* get 'bridging' between pins - just use good solder wick to
remove the surplus, I recommend Chemtronics 'SODER WICK' - best wick I've
ever come across.

Maybe I'll post an example of what you can do this way at a.b.s.e if you're
interested ?

Graham

 

[Rene Tschaggelar]

Hello
Can someone recommend a soldering/manufacturing service that will do
a small soldering job for me. Just 2 ICS: one TSOP 44 pin and a TQFP
144 pins. Well there is no solder mask on the PCB, so I think they have
to be soldered manually instead of using wave soldering.

Do it yourself with flux gel. A wide iron, 1.5mm, with
a drop of tin does 5 pins at once and the boiling flux
gel removes the bridges. If you etch yourself, do yourself
a favour and make the footprint pads at least 100 mils long.
This would allow to wipe the tin away from the chip.

Rene

 

[[email protected]]

Pace make a tip with a small well to hold a blob of solder, several
others have copied it, you just run it down the row of pins. the trick
is to have the right amount of flux on the pins. Practice! start with
the packages with the widest pin spacing and work down as you get the
technique.

 

[Leon Heller]

Hello
Can someone recommend a soldering/manufacturing service that will do
a small soldering job for me. Just 2 ICS: one TSOP 44 pin and a TQFP
144 pins. Well there is no solder mask on the PCB, so I think they have
to be soldered manually instead of using wave soldering.

Metcal makes a cartridge with a mini hoof tip for drag soldering. It works
very well, even on parts with 0.5 mm lead spacing.

Leon

 

[Paul Olley]

One such company is http://www.pcbtrain.co.uk/assembly.htm

I haven't used them myself.

Like the other posters I agree that it is quite feasible to solder it
yourself.

A good amount of flux is the thing that did the trick for me.

For around £5 I bought a bottle of "Future 315 Low Residue Flux"
(www.warton-metals.co.uk) I used a syringe to flood the (tinned) pads
before placing the 80 PIN TQFP. Soldered two diagonally opposite pads
before doing the rest. (This was the most difficult step, to get the
alignment exactly right!) My technique was to load the soldering iron
tip with a very small amount of solder and then to touch it to the pad
and pin with just a little pressure. The flux has the effect of making
the joint pretty much instantly. The flux tended to evaporate quickly,
so I just syringed more. I used an Antex M12 soldering iron, with a
very small tip that I had filed down a little to make a very fine
point. A magnifying glass from a set of "helping hands" was necessary
to make the pins clearly visible.

As I recall I only had one solder bridge, easily removed with solder
wick. Another popular technique is the "flood it with solder and then
remove it with wick" approach, which I haven't tried.

The only pins that didn't have a connection were I couple that I had
omitted to solder!

Paul.

 

[Walter Harley]

[...] Soldered two diagonally opposite pads before
doing the rest. (This was the most difficult step,
to get the alignment exactly right!) [...]

I've had some success with first wetting a corner pad with a bit of solder.
Then, while using the soldering pencil to keep that solder melted, hold the
component with tweezers, place it in the desired location, and finally
remove the soldering pencil.

That works very well on SOIC16 and smaller. I haven't tried soldering
anything with a finer pitch than that, but I don't know why it wouldn't
work.

I have been tempted to try the "toaster oven reflow" technique, but the high
price of solder paste has prevented me. (I suppose it's cheaper in larger
quantities, but last time I looked it was going to cost something like US$65
to purchase the smallest quantity I could find, including the syringe and
the required overnight shipping.) Hand-soldering has proved very easy,
though.

 

[Paul Olley]

I looked into the solder paste "toaster over" scenario. I found
www.farnell.com (search for "solder paste") stocks it in a syringe for
around £9, that's around US$16 Perhaps try at www.newark.com

 

[Paul Burke]

That works very well on SOIC16 and smaller. I haven't tried soldering
anything with a finer pitch than that, but I don't know why it wouldn't
work.

SOIC16??? That's HUGE, I do those quite happily with the big tip iron
and a pair of tweezers. It's the little buggers, 0.5mm pitch say, and
the ones without any noticeable lead at all (the ones with a metal slab
on the bottom too, forget the name) that make life harder. Not to
mention BGA....

Paul Burke

 

[Walter Harley]

SOIC16??? That's HUGE, I do those quite happily with the big tip iron and
a pair of tweezers. It's the little buggers, 0.5mm pitch say, and the ones
without any noticeable lead at all (the ones with a metal slab on the
bottom too, forget the name) that make life harder. Not to mention BGA....

Yes, the ones with the metal on the bottom (TI's PowerPad, for instance) are
what make me think that sooner or later I'm going to have to figure out the
toaster oven method.

For now, I'm getting along fine with SOIC, SOT-23, etc.; all of the
components I need to use are available in those form factors (though not DIP
any more).

 

[Paul Burke]

Yes, the ones with the metal on the bottom (TI's PowerPad, for instance) are
what make me think that sooner or later I'm going to have to figure out the
toaster oven method.

I've mastered the FN(?) package, though it's fiddly. When laying out,
put a hole in the base pad, large enough to get the tip of a fine bit
through. Flux everything. Solder blob one corner pin, and anchor the
component in place with that. Solder the other pins (fiddly). Then
introduce solder through the underside hole gently, so it acts to
conduct heat to the bottom pad. When it's ready, it wicks in, and all is
OK. I've only tried it with quite small components, the LTC2601 being
the smallest, but it works fine for them.

Paul Burke

 

[Spehro Pefhany]

I've mastered the FN(?) package, though it's fiddly. When laying out,
put a hole in the base pad, large enough to get the tip of a fine bit
through. Flux everything. Solder blob one corner pin, and anchor the
component in place with that. Solder the other pins (fiddly). Then
introduce solder through the underside hole gently, so it acts to
conduct heat to the bottom pad. When it's ready, it wicks in, and all is
OK. I've only tried it with quite small components, the LTC2601 being
the smallest, but it works fine for them.

Paul Burke

Hot air works okay for them too, at least for a few prototypes. I have
not tried a QFN44 or 28 yet, but they don't look too scary.



Best regards,
Spehro Pefhany

 

[Walter Harley]

Hot air works okay for them too, at least for a few prototypes. I have
not tried a QFN44 or 28 yet, but they don't look too scary.

I'm assuming we're all talking about the same thing, chips with a heat-sink
pad in the center that is intended to be soldered directly to a pad on the
component side of the PCB, that in turn is connected with thermal vias to
more copper on the other side of the PCB. The problem being that the pad is
between PCB and chip, and therefore not accessible.

How do you get solder to the hidden pad? And, are you applying the hot air
from the component side or the other side?

I like Paul's idea of leaving a hole big enough to get the solder in from
the bottom.

 

[Fred Bartoli]

I'm assuming we're all talking about the same thing, chips with a heat-sink
pad in the center that is intended to be soldered directly to a pad on the
component side of the PCB, that in turn is connected with thermal vias to
more copper on the other side of the PCB. The problem being that the pad is
between PCB and chip, and therefore not accessible.

How do you get solder to the hidden pad? And, are you applying the hot air
from the component side or the other side?

I like Paul's idea of leaving a hole big enough to get the solder in from
the bottom.

The pad in itself won't do much for power dissipation. You have to connect
it through a bunch of vias to some plane that'll spread heat across the PCB
more efficiently.

As Paul said, make one or more vias bigger so that you can solder the
package through them.