On Sat, 20 Mar 2004 14:37:46 -0800, Suri <hsuri@usc.edu> wrote:

>I am making a pcb for a robotics board and am debating the use of either 
>a MLF64 package pr a TQFPK64 .the advantage of using the MLF64 is size 
>reduction.
>
>the question is:
>--Can MLF64 be soldered by hand using a normal soldering station. or 
>should i spend the extra money to get it soldered from the PCB manufacturer?
>
>I do know that the TQPK package is doable by hand.
>
>--has anyone here soldered a MLF package by hand?
>
>thankyou

I have had great sucess in soldering MLF components by hand using a
normal solering iron. I extend the standard footprint pads with 0.5mm.
This provides a accesable thermal contact point for the solder iron
tip. It also makes it a lot easier to probe during development. Even
with this extended footprint, the MLF is a great deal smaller than the
TQFP.

Regards
   Anton Erasmus

Yes I do it.
It's a bit tricky but not a major problem. if you can solder a SMD IC with
.050" pitch pins OK, your in business.
I have done it quite a number of times using Atmel Atmega8 and Atmega128 MLF
packages and Analog Devices Accellerometer chips.
I use liquid non-corrosive flux (GC Electronics #10-4202) for all my SMD
work. The flux is extremely extremely important.
You cannot do it without flux, it is not going to happen.
Another help for success is to use www.expresspcb.com printed circuit
boards. ExpressPCB nicely solder tins all the traces and pads making it a
big help too. Trying to tin those tiny .050" pitch pads by hand really
sucks.
You also have a center pad on the chip that needs soldering too. I make the
pad and have a .020" via to the other side to another pad on the bottom of
the PCB.

Anyway, after getting a PCB done, you put a thin tiny droplet of flux on the
center pad, then apply flux to all the pin pads.
Wait a few minutes for the solvent to evaporate to make it nice and sticky.
This is a personal preference sort of thing. Some people like it more sticky
or less sticky.Then you carefully place the MLF package on the PCB, using a
head magnifier and a X-acto knife bade tip. Carefully align the chip on the
pads. You can see along the edge of the chip where the edges of the pads
are, making it easy to align the pins. Then when satisfied, carefully push
down on the chip to push it into the flux and PCB to help hold it in place.
Then double check the pin positions carefully again. Next while holding the
chip down with the X-acto knife blade, you take the soldering iron tip and
heat up the pads, you can see the solder melt as the flux sizzles some. I
usually hold the soldering iron tip up as close to the MLF package pins as I
can get it.
I use a regular sized more or less blunt iron tip, it can solder two or
three pads or traces at the same time. It applies more heat to the pads
ensuring a solder connection occurs. Then I turn over the PCB and apply some
soder so it wicks through the via on the bottom to solder the center pad on
the chip. This takes a little longer as your trying to get the center pad to
stick to the chips center pad.
I usually build up just enough of a PCB to be able to test the chip to
ensure I can program and get thechip to do something light excersize a LED
or something. At first until you get the hang of it you might have to reheat
some of the connections to get contact for a pin or two that didn't get
soldered the first time. Don't overdi\o the heat though. the chips can take
a lot of heat as the IR ovens heat them up good and toastie already, but you
don't want to have the pads get damaged too much.

The flux is extremely important it helps to solder the connections, but most
importantly it prevents solder bridges form forming.
You have to have the flux. I guarantee it will not work without the flux.
Don't even bother to try it without the flux. The flux that comes inside a
piece of solder wire will not work. You gotta have the flux to make it work.

I put some photos up on the
http://photos.groups.yahoo.com/group/megabitty/vwp?.dir=/NanoSumo+Bots/Earl%27s+bot&.src=gr&.dnm=Atmega8+MLF+with+402+size+LEDs.jpg&.view=t&.done=http%3a//photos.groups.yahoo.com/group/megabitty/lst%3f%26.dir=/NanoSumo%2bBots/Earl%2527s%2bbot%26.src=gr%26.view=t
Yahoo groups Meagbitty site that shows a tiny less than 1" robot board for
Nano-Sumo that I did. it uses the incredibly tiny 402 size LED's and other
parts as well. What is really really hard is trying to identify the anode
and cathode on a 402 size LED.  Now that is hard.  Especially when you get
in backwards and you have to remove it and turn it around and resolder it.
:)

Personally, on the Atmega8 MCU's a TQFP and a MLF part doesn't save any PCB
space on the board. The trace fanout to run the traces around sort of
defeats the purpose. But if your mass producing PCB's the costs savings is
more significant then.



"Suri" <hsuri@usc.edu> wrote in message news:c3ih1n$stv$1@gist.usc.edu...
> I am making a pcb for a robotics board and am debating the use of either
> a MLF64 package pr a TQFPK64 .the advantage of using the MLF64 is size
> reduction.
>
> the question is:
> --Can MLF64 be soldered by hand using a normal soldering station. or
> should i spend the extra money to get it soldered from the PCB
manufacturer?
>
> I do know that the TQPK package is doable by hand.
>
> --has anyone here soldered a MLF package by hand?
>
> thankyou
>

You cannot solder an MLF package with a pencil iron.  There
construction is somewhat like BGA, where the leads are on the bottom
of the package.  One option is to use solder paste, and flow the board
in an oven.  Take a look at
http://www.stencilsunlimited.com.  The stencil isnt necessary, I've
actually used a syringe to apply paste to the individual pads instead.
Be aware that these MLF packages are ultra fine pitch, and good
soldering experience is necessary.  Even then, prepare to get some
"rejects."

If you have an option to get the boards professionaly assembled, I
would go that road, but soldering MLF packages is possible for the
hobbiest.

-J


Suri <hsuri@usc.edu> wrote in message news:<c3ih1n$stv$1@gist.usc.edu>...
> I am making a pcb for a robotics board and am debating the use of either 
> a MLF64 package pr a TQFPK64 .the advantage of using the MLF64 is size 
> reduction.
> 
> the question is:
> --Can MLF64 be soldered by hand using a normal soldering station. or 
> should i spend the extra money to get it soldered from the PCB manufacturer?
> 
> I do know that the TQPK package is doable by hand.
> 
> --has anyone here soldered a MLF package by hand?
> 
> thankyou