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cool surface mount technique

Q

Quack

Jan 1, 1970
0
After trying lots of different ways to mount SM chips, i think i have
found the easiest and fastest way, without applying to much heat to
the chip, or fiddling around under microscopes etc.

My boards are made using blue PNP on a 600dpi laser printer, and
etched with ferric chloride chrystals desolved in warm water.

First clean the board perfectly, using some cleaning alcohol (after a
good scrub in the sink to remove any discoloration). Once is nice and
shiny, apply a coating of 'flux 140' to the entire board.
This protects it from oxidization and also contains some flux to help
things along. (this can be purchased from RSWWW in UK, part#363-6539
£7.29).

Wait for this to dry completely (usually left overnight).

Now for the actual soldering;

Add a little solder to the iron, but only a LITTLE, just enough to
paint it - no blobs hanging off.

now use the iron to 'paint' the pads where the SM chip will sit - just
make them go silvery. If you prepared your iron properly, not using
too much solder, there will be no shorted pads, they should look just
like they started, except silvery.

now place the chip carefully (some people may need magnification here
like me :), depending on the exact size of the chips) - now use
something like a pen or small screwdriver to press lightly on the top
of the chip holding it in place with one hand.

lightly and quickly touch the top of each pin using a clean SOLDERLESS
iron.

and presto - done!.

the solder on the pad itself heats fast enough to bond with the legs,
no shorts, no messy flux or solder removing braid.
and the chips dont even get warm! no damage.

checkout some example pictures here of the latest board i made using
this technique, works perfectly for me!

(i use a WELLER standard tip, nothing special for my iron)

www.quack.cc/board1.jpg
www.quack.cc/board2.jpg
www.quack.cc/board3.jpg
www.quack.cc/chips.jpg

I may take some snapshots and make a step-by-step html page for the
next board i make. But i think its pretty self-explanatory, but
perhaps for a begining to end kind of guide.

Good luck :)
 
J

Jerry Greenberg

Jan 1, 1970
0
Using your method:

How do you work with the devices that use 1/100 of an inch spacing
between the pins?

How do you handle the new components that are 1/10 of in inch long and
1/20 of an inch wide?

For the 1/10 inch pin spaced IC's, I can see this being done, but very
carefully.

Jerry Greenberg
http://www.zoom-one.com
 
Q

Quack

Jan 1, 1970
0
Using your method:
How do you work with the devices that use 1/100 of an inch spacing
between the pins?

The smallest i have used was the above P15V 'video switch' chips, they
are .025 spacing between the pins, and .008 pin width (not sure how
that equates to inches).

How do you handle the new components that are 1/10 of in inch long and
1/20 of an inch wide?

For the 1/10 inch pin spaced IC's, I can see this being done, but very
carefully.

Actually i tried the other tricks (read lots of little tips and
techniques by searching through google). And this was by far the
easiest.

I dont see why it cant be done with much smaller chips - given perhaps
a better viewing arrangement..
As the soldering iron contains no solder at the point of contact,
there are no shorts that occur - and so the iron can touch multiple,
if not all pins at once.
as long as the tracks where prepared nicely - which is suprisingly
easy todo once coating the 'flux 140', just a touch and they all go a
nice silver.

Actually it would be good to see someone else try it and give their
opinion.. :)


Alex.
 
C

Charles Jean

Jan 1, 1970
0
The smallest i have used was the above P15V 'video switch' chips, they
are .025 spacing between the pins, and .008 pin width (not sure how
that equates to inches).



Actually i tried the other tricks (read lots of little tips and
techniques by searching through google). And this was by far the
easiest.

I dont see why it cant be done with much smaller chips - given perhaps
a better viewing arrangement..
As the soldering iron contains no solder at the point of contact,
there are no shorts that occur - and so the iron can touch multiple,
if not all pins at once.
as long as the tracks where prepared nicely - which is suprisingly
easy todo once coating the 'flux 140', just a touch and they all go a
nice silver.

Actually it would be good to see someone else try it and give their
opinion.. :)


Alex.


Alex

I saw your method and think its really neat. No excess solder to
cause any bridging, just enough to connect the part to the board. I'm
getting ready to learn SMT, and will probably start with this
approach. Could I use a 600 dpi inkjet printer instead of the
laserjet? Could you please post a USA source for the Flux 140?

BTW, I did a search for SMT fluxes right after I read your post, and
found a very interesting product put out by Kester-PN TSF6516-a "Tacky
Solder Flux", designed to paint on SMT component leads and be tacky
enough to hold them on the board prior to reflow soldering. I'm
thinking one could prepare the board the way you do, apply ALL the
SMTs to the board via the TSF compound, then reflow the whole board in
a toaster oven(this has been done!). This would give you a little
"wiggle room" when placing each device-you could always adjust it on
the board with tweezers, etc., until it is positioned just right. Do
you think the Flux 140 would be sticky enough to do the same thing?

I also thought about tinning the copper traces, but have heard bad
stories abut that stuff. Better to coat it with solder. How about
getting to the point where the Flux 140 has been applied and dried,
then dip the whole board in a solder bath? Wonder if bridging would
cause a mess with this scenario?

I'm looking around now for a good used 30X stereo zoom dissecting
microscope. What next-die bonding and wire bonding on the PCB?

Charlie

If God hadn't intended us to eat animals,
He wouldn't have made them out of MEAT! - John Cleese
 
N

N. Thornton

Jan 1, 1970
0
The smallest i have used was the above P15V 'video switch' chips, they
are .025 spacing between the pins, and .008 pin width (not sure how
that equates to inches).

I dont see why it cant be done with much smaller chips - given perhaps
a better viewing arrangement..


I wonder if one mounted a short scalpel blade in an iron, and possibly
turned the iron temp up, whether it would be possible to do much finer
pitch work. Havent tried it.

Regards, NT
 
Q

Quack

Jan 1, 1970
0
Hi Charlie,
Could I use a 600 dpi inkjet printer instead of the
laserjet?

I use "blue Press'n'Peel transfer paper" (www.techniks.com) which says
'laser or photocopier' on the instructions. I think it specifically
needs the toner to make the transfer - i have never tried anything
with an inkjet.
But a good photocopier (set to fairly dark) should produce quite well
too, although i havent tried that either.

I used to use kodak 'photo paper' (same laser printer) - cheaper than
PnP, its okay for normal work but cant get the resolution for SM
layouts.
(usually using photo paper i always had to make some minor fixups with
a pen afterwards - these fixups are pretty rare using the PnP film)
Could you please post a USA source for the Flux 140?

Google doesnt return anything obviouse, im really not sure.
its made by "seno", the bottle has german + english writing on it.
Here's a pic; www.quack.cc/flux140.jpg

BTW, I did a search for SMT fluxes right after I read your post, and
found a very interesting product put out by Kester-PN TSF6516-a "Tacky
Solder Flux", designed to paint on SMT component leads and be tacky
enough to hold them on the board prior to reflow soldering. I'm
thinking one could prepare the board the way you do, apply ALL the
SMTs to the board via the TSF compound, then reflow the whole board in
a toaster oven(this has been done!).

sounds great!, i'll have to experiment with that if im going to make
boards with a lot of SM components - could save lots of time.

Do you think the Flux 140 would be sticky enough to do the same thing?

the flux140 is slightly sticky - although it does dry up after a full
day or two. I guess it depends how much of a coating you slop on :)

I doubt it would be too good for oven reflowing, but having never done
any oven work - i wouldnt really know for sure.

I also thought about tinning the copper traces, but have heard bad
stories abut that stuff. Better to coat it with solder.

Yeah, i baught some chemical tinning mixture and tried that on a few
boards. It made them go nice and silvery, but i was very disapointed
when i went to solder it!

I had to heat things up SO much to have the solder run nicely it was
ridiculous.
The solder just wouldnt touch the pads until the soldering iron was
touching the pad for a good 5 seconds, then it would flow on (and
unevenly, not very pretty at that).

this could have been because after the tinning (then cleaning) process
i coated the board in flux140 (which usually makes the boards really
easy to work with).
Pherhaps the flux140 is designed to work on copper, but not tin.
strange effect anyway - i wont be doing that again :).


How about
getting to the point where the Flux 140 has been applied and dried,
then dip the whole board in a solder bath? Wonder if bridging would
cause a mess with this scenario?

I havent used a solder bath before - but it could be an interesting
way of doing it - especially if you left the 'resist' on the tracks,
and just removed it from the pads where the components would go ...
(could be tricky).

What next-die bonding and wire bonding on the PCB?

whats that ? i havnt heard of them :)

Im not a PCB expert by any means, i have only been making boards for
about a year and have settled nicely into my routine for making small
batches. But as work increase i do need to look at new techniques to
move things along a little quicker.

But then again, if its something that will be made in larger qty's,
there are always the profesionals todo it for you.
(and in larger qty's the cost is still low per board, just saves a
whole lot of time)

Im glad you liked it, i think i will knock up that web page after all
then.

Alex.

PS: i am not affiliated with SENO/flux140 - not trying to sell it or
push it - i just find it really useful :), no reason this cant be done
without it.
 
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