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PICList Thread
'[EE]: home SMD'
2002\12\10@111311 by Roman Black

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Tim Crist wrote:
>
> I've only been watching this thread with one eye open, but this is a really
> cool idea Roman...  Here are a couple of questions for you:

Ok, well i'm only a baby in SMD, there are guys
here doing it a lot longer than me! :o)
These tests I did recently as part of a production
problem, i've been working very busily trying to
get a batch made before the hols.

I did time trials of all our through-hole processes
ie cut tape, bend legs, insert, hold, flip board
solder, snip legs etc and the hand SMD work is
faster for all parts than through hole. :o)


> How do you get the solder paste down? Syringe?  Squeegee w/solder paste
> screen?

Syringe hand held, about 1-2 seconds per part for
2 dot parts. I've done screen printing years ago
and will probably go screen if we do SMD production.
Screens only cost about $150 USD to make if you shop
around.


> Where do you buy the paste, and what kind do you recommend?

Again you're asking the wrong person, only bought
one type from Farnell and had probs. I heard
Kester brand is better?

> Do you use the toaster oven for reflow?

Yes. Small stainless cabinet 4 element 1500W oven,
cheap and nasty. Has a couple of cold spots (needs
a fan?) but I know where they are and can do the
soldering just by turning the knob and watching the
clock. But I did do tests first with IR thermometer
and checked it all out. With a bit of experience you
can judge by the solder paste appearance.

Maybe someone will make a PIC oven controller using
the common $5 Sharp thermistor I posted about? ;o)

> What's the finest pitch you feel comfortable with?

Again i'm only a baby, wouldn't want to fiddle with
anything under 0805 or SOIC. Suppose I would go to
the quad pack chips but probably not 0603. :o)


> I want to move up from the 8 to 10 sec/part placement too!

The vac pickup tool is the main thing, and using
tapes means there is never a part upside down, or
rotated wrong, or on top of another part. That speeds
it up a lot!
-Roman


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2002\12\10@131409 by Roman Black

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Good beginner SMD toaster oven link:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm

Does anyone want to take on the challenge of
hooking a 16F628 (or 16F84) up to a thermistor
and triac to make a cheap SMD oven controller?? ;o)
-Roman

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2002\12\10@133035 by Peter L. Peres

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On Wed, 11 Dec 2002, Roman Black wrote:

*>Good beginner SMD toaster oven link:
*>www.seattlerobotics.org/encoder/200006/oven_art.htm
*>
*>Does anyone want to take on the challenge of
*>hooking a 16F628 (or 16F84) up to a thermistor
*>and triac to make a cheap SMD oven controller?? ;o)

How about you ? ;-)

Peter

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2002\12\10@143606 by Wagner Lipnharski

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Roman Black wrote:
> Good beginner SMD toaster oven link:
> http://www.seattlerobotics.org/encoder/200006/oven_art.htm
>
> Does anyone want to take on the challenge of
> hooking a 16F628 (or 16F84) up to a thermistor
> and triac to make a cheap SMD oven controller?? ;o)
> -Roman


Doing that already with an (fast and cheapper) AVR... sorry, no PIC  :)

Using a 30k Thermistor, also tested with 3 x 1N4148 diodes as sensor
temperature.
PWM output controlling a solid state relay (ZC).  Could be using a Triac
(400V @ 25A) and a ZC optocoupler to avoid current noise.  A simple PWM
over a cap and comparing the thermistor voltage, gives me a perfect linear
ADC ramp.  This successive aproximation ADC takes some time to react (tens
of milliseconds), but it is more linear and nothing is in a rush in the
oven anyway.  Everything was built into a power outlet box, one led and one
N/O button. Pressing the button starts the soldering profile, 7 minutes, 2
minutes colling down, buzzer at 9th minute to signal to open oven's door,
wait a minute or so and remove the boards.  2 or 3 boards per coocking
batch, 12 to 18 boards per hour, not bad for a kitchen job.

Right now I am thinking to produce a continuous soldering oven.  A three
stage long oven (4 ft long), 200, 325 and 450°F sections with continuous
heat system, and a cooling down chamber at the end to avoid component
cooling stress. Small doors could be made between the sections if
necessary. The big chalendge now is the transport system that should stand
high temperatures.    Need to find out some polimer or flex material that
can stands at least 550°F to build the moving belt.  It should be steady,
no bumps or jumps.

minutes------>
0    1    2    3    4    5    6    7    8
|    |    |    |    |    |    |    |    |
--------------------------------------------------> exit
|___________________|_________|____|____|         \
      200°F           325°F   450F 150F          |
|<-------------48 inches--------------->|         /
                                          <-----'  belt
 -->|    |<--- 6 inches

Belt moves continuously 6 inches/minute.
Every minute 2 unsoldered boards are loaded at left and 2 soldered boards
cooling down (around 200F) are removed from the right.  2 boards per
minute, 120 boards per hour. Not bad for a home made continuous soldering
overn.

Though also about a rotative oven, a round metal plate rotating into
different temperature round chambers, one slot open to remove/deposit
boards.  It will solve the belt problem.

Any suggestions?

Wagner.

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2002\12\10@151048 by Josh Koffman

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Recently some of the kitchen type stores around here have begun selling
silicone shaped into oven mits. They say it can stand huge temperatures.
If you could get some in a sheet form, it may do the trick for the belt.
Plus it seems slightly soft and grippy, so the boards wouldn't slide
around too much hopefully.

Josh
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Wagner Lipnharski wrote:
> Right now I am thinking to produce a continuous soldering oven.  A three
> stage long oven (4 ft long), 200, 325 and 4500F sections with continuous
> heat system, and a cooling down chamber at the end to avoid component
> cooling stress. Small doors could be made between the sections if
> necessary. The big chalendge now is the transport system that should stand
> high temperatures.    Need to find out some polimer or flex material that
> can stands at least 5500F to build the moving belt.  It should be steady,
> no bumps or jumps.

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2002\12\10@162245 by steve

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> Right now I am thinking to produce a continuous soldering oven.

I've thought about this one too. A couple of places to look into -
Commercial toast making machine and printers that do embossed
printing the old fashioned way (eg. Wedding invitations). Both of
these use a chain link style of conveyor with a heating element.
Either of them would do fine.
Rather than make it really long, I was thinking of a mix of two (or
more) temperature compartments and stopping and starting the
belt to get the profile. Add red and green lights to say when to put
the next board on the belt.


Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: .....stevebKILLspamspam@spam@tla.co.nz      fax +64 9 820-1929
======================================================

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2002\12\10@171501 by lexandre_Guimar=E3es?=

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Hi, Wagner

> Doing that already with an (fast and cheapper) AVR... sorry, no PIC  :)
>
> Using a 30k Thermistor, also tested with 3 x 1N4148 diodes as sensor
> temperature.
> PWM output controlling a solid state relay (ZC).  Could be using a Triac
> (400V @ 25A) and a ZC optocoupler to avoid current noise.  A simple PWM
> over a cap and comparing the thermistor voltage, gives me a perfect linear
> ADC ramp.  This successive aproximation ADC takes some time to react (tens
> of milliseconds), but it is more linear and nothing is in a rush in the
> oven anyway.  Everything was built into a power outlet box, one led and
one
> N/O button. Pressing the button starts the soldering profile, 7 minutes, 2
> minutes colling down, buzzer at 9th minute to signal to open oven's door,
> wait a minute or so and remove the boards.  2 or 3 boards per coocking
> batch, 12 to 18 boards per hour, not bad for a kitchen job.

   Are you thinking about making the desing public ??? I would love to use
it to one more oven that I have sitting still without the temperature
controller.. Please do not tell anybody here, but I also use AVR's much more
than PIC's :-)

> Right now I am thinking to produce a continuous soldering oven.  A three
> stage long oven (4 ft long), 200, 325 and 450°F sections with continuous
> heat system, and a cooling down chamber at the end to avoid component
> cooling stress. Small doors could be made between the sections if
> necessary. The big chalendge now is the transport system that should stand
> high temperatures.    Need to find out some polimer or flex material that
> can stands at least 550°F to build the moving belt.  It should be steady,
> no bumps or jumps.

   I am sorry to disapoint you on that one but you would need at least a 7
zones oven to get close to the right temperature profile !!! I made some
tests with 3 zone comercial infrared SMD ovens and my small kitchen oven
works much better on the temperature profile side ! I would just use more
small ovens or go to a outside manufacturer if that does not give me the
necessary production. It is worth to do it for small batch runs but the
problems that arrise with bigger productions are not worth it to handle "in
house". It get's so cheap on bigger productions that I can not think of any
reasons to keep it inside my business for bigger productions.

   If you really want to go for it I would just get a replacement conveyor
belt from a reflow oven manufacturer !! They are made of stainless still and
are like a mesh. Silicone will not handle the temperature for too long, it
will crack with continous use. The only option is metal and you can not just
use a metal belt because it will "suck" the heat. The mesh stuff is what is
used in all ovens I have seen.

Best regards,
Alexandre Guimaraes

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2002\12\10@173301 by Peter Homann

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Already done. Have a look at:

http://www.iis.com.br/~alexg/oven.pdf


Peter Homann
Peter.HomannspamKILLspamadacel.com
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
http://www.adacel.com <http://www.adacel.com>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 665


{Original Message removed}

2002\12\10@174750 by lexandre_Guimar=E3es?=

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Hi, Peter

> Already done. Have a look at:
>
> http://www.iis.com.br/~alexg/oven.pdf

   I made the web space available but really did not look too much at it
:-( What a shame on me...

   Does it take care of the full profile or it just gets to the set
temperature ?? By the little I looked I understood that it just got to a
preset temperature and turned the heat off and the fan on. For the solder to
be ok, we need all the temperature "ramps" that are in the manufacturers
datasheets. I can tell by practice that those ramps are really necessary to
get good and reliable solder joints.

Best regards,
Alexandre Guimaraes

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2002\12\10@180739 by Wagner Lipnharski

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Peter Homann wrote:
> Already done. Have a look at:
>
> http://www.iis.com.br/~alexg/oven.pdf
>
>
> Peter Homann


I saw it in the past few weeks. That is not a profile temperature
controller, it just follows a manual preset temperature adjustment, like an
electronic thermostat, am I wrong? please correct me.

Wagner.

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2002\12\10@181357 by Peter Homann

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Alexandre ,

It does not have the temp ramps. That said, the rise in temperate is slow
enough that it sits in the pre heat temperature range long enough to
evaporate the solvents out of the paste.

The problem I had is that there are only about 11 words left in the PICF84
memory. My next job is to replace it with a PICF628, doubling the memory.
That way I can program the ramp in.

Alternatively, once the temp reaches the preheat value pressing the
start/stop will turn off the heaters, pressing it again will turn them back
on to continue heating.

I'm very interested in a continuos machine. I'm sure the continuous toasting
machines could be adapted. The small commercial belt machines have a bay
with the preheat heater elements, the belt then moves the board to the
soldering bay with the big heaters. The length of the bays need to be the
correct ratio to ensure the board is in the bay for the appropriate time.

cheers,


Peter Homann
.....Peter.HomannKILLspamspam.....adacel.com
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
http://www.adacel.com <http://www.adacel.com>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 665


{Original Message removed}

2002\12\10@191713 by Wagner Lipnharski

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Alexandre Guimarães wrote:
{Quote hidden}

I don't see why not make it public.
It will require calibration for any particular oven, or thermistor, or
diodes, anyway.


{Quote hidden}

I understand that holding temperature in each chamber (zone) would be a
pain in the neck.

    DOOR1       DOOR2       DOOR3
      X           X           X
ZONE1  X   ZONE2   X  ZONE 3   X  ZONE4 (COOLING)
      X           X           X

Of course the advantage of a continuous belt allows a faster production,
but this you can also do using individual toster ovens.  A 3 zone
continuous oven (like above) would produce 120 boards per hour, but you can
do almost the same with 10 kitchen toasters with controlled profile
temperature.  The advantage of the toasters is that you don't need to use
them all, use only what is necessary, and if some blows up, you still
working with the remaining.  The disavantage is the huge loss of energy,
since in a continuous belt system, you can build up a very good thermal
insulation and use the energy efficiently.

For example, using heavy metal walls, it will store thermal energy and will
work as a thermal filter, even opening doors for seconds it will not drop
much temp degrees per chamber.  External insulation will avoid thermal loss
through the walls. Heating elements could be inserted in middle of the
walls.

I am not expert (or other) in thermal systems, but I think that keeping
450°F in an enclosed insulated chamber expend less energy than heating to
450F, cooling down, heating again, cooling down again, as happens in a
conventional kitchen toaster.  The toaster walls are done weack in
insulation, on purpose, to helps to cool down and helps the thermostate to
control the temp.  In the regular toaster, if you heat a pizza at 350F than
immediately needs to cook something else at 200F, in 30 or less seconds the
toaster will drop from 350 to 200F. If done with heavy and insulated walls,
it could take 5 minutes or more to cool down like that.

The continous belt system, will expend energy continuously for 3 zones,
probably around 1200W (zone3), 800W (zone2), 400W (zone1), total 2400W/h.

Using 10 toasters, will spend  1200W/1minute, 800W/2minutes, 400W/4minutes,
in a total of 10 minutes cycle, it means 6 times in an hour, or 1200W/6
minutes, 800W/12minutes, 400W/24minutes, or, 4400W/6minutes, 440W/h, times
10 toasters, 4400W/h.

The continous belt will not spend the whole 2400W/h since temperature loss
is reduced, but the toasters will in fact consume 4400W/h.

Somebody in the list expert in thermal metalurgy?
What about a vertical oven? How tall a vertical heavy metal tube should be
to heat at 450F on the top and 200F at the bottom, by convection effect?
Several circular heaters could be installed from bottom to top. The normal
small air flow into the tube will also helps to push heat up.  A vertical
belt with mesh horizontal platforms could lift boards into the tube in such
way that the profile temperature would be achieved along the transport.  A
fast door on top will open to allow the mesh platform to lift a board out
the tube, and also will allow a small quantity of hot air to get out,
helping to push heat up and allowing to control (cool down) few degrees the
whole system, helping the electronic auto-thermal control to operate and
not heating so much the very top.

                |
       \        |       /
        \       |      /
         \..========../
exit     //          \\
<---cccc  H            H
  -------H            H\
         H            H \
         H            H  \
   cccc  H            H   \
  -------H            H
         H            H\
         H            H \    belt
   cccc  H       BELT H  \   down
  -------H            H   \    |
         H            H        |
         H            H        |
X=DOOR=== H ||         H        V
||        H || very    H\
||  ssss  H || hot     H \
|| -------H || <---    H  \
||        H ||         H   \
||        H || OVEN    H
||  hhhh  H ||<---     H\
|| -------H ||         H \
||        H ||         H  \
||        H ||         H   \
||  hhhh  H || hot     H
|| -------H || <---    H\
||        H ||         H \
||        H ||         H  \
||  wwww  H ||         H   \
|| -------H ||         H
||        H ||         H\
||        H ||         H \
||  wwww  H ||         H  \
|| -------H || warm    H   \
||        H || <---    H
X=DOOR=== H ||         H\
         H            H \
   uuuu  H            H  \
  -------H            H   \
         H            H
         H  A         H\
   uuuu  H  |         H \
  -------H  |         H  \
         H  up        H   \
         H            H
--->uuuu  H            H\
  -------H            H \
entry     \\          //  \
          \\========//\   \
         /      |      \
        /       |       \
       /        |        \


uuuu = unsoldered, cool.
wwww = warming up
hhhh = heating up
ssss = soldering
cccc = cooling down

The belt goes into the heating chamber, entering by the bottom, exiting at
the top.
Is it too stupid, or it could work?

Wagner.

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2002\12\10@212255 by lexandre_Guimar=E3es?=

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Hi, Wagner

> I don't see why not make it public.
> It will require calibration for any particular oven, or thermistor, or
> diodes, anyway.

   All right... I will like to see that, it will save me a few bucks and I
can taylor it to my needs. We all profit something when we share knowledge
:-)

> I understand that holding temperature in each chamber (zone) would be a
> pain in the neck.

   The problem is not holding the temperature in each chamber, it is
getting the right profile on the board itself. With a 3 zones oven you will
have a heck of a time to achieve that. I saw 3 comercial designs and they
all failed badly to get a nice profile to the boards !! That is the main
reason the bigger ones have 7 or even 9 heat zones !

> Of course the advantage of a continuous belt allows a faster production,
> but this you can also do using individual toster ovens.  A 3 zone
> continuous oven (like above) would produce 120 boards per hour, but you
can
> do almost the same with 10 kitchen toasters with controlled profile
> temperature.  The advantage of the toasters is that you don't need to use
> them all, use only what is necessary, and if some blows up, you still
> working with the remaining.  The disavantage is the huge loss of energy,
> since in a continuous belt system, you can build up a very good thermal
> insulation and use the energy efficiently.

   Yes, it would be more energy efficient but have you checked on how much
energy you are really using with the small oven ?? It is not as bad as you
may think. The air conditioning costs much more !

> For example, using heavy metal walls, it will store thermal energy and
will
> work as a thermal filter, even opening doors for seconds it will not drop
> much temp degrees per chamber.  External insulation will avoid thermal
loss
> through the walls. Heating elements could be inserted in middle of the
> walls.

   If you get up to the point where energy managment is that important I
would strongly advise that you buy a ready made reflow oven ! The companies
that manufacture those have dealt with all problems that arise from the
different reflow zones, isolation, speed, conveyors and everything else. If
you need a fast production the market has all kinds of products to offer,
from the cheap ones to the big and fast beasts !

Best regards,
Alexandre Guimaraes

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2002\12\10@213218 by lexandre_Guimar=E3es?=

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Hi, Peter

> Alexandre ,
>
> It does not have the temp ramps. That said, the rise in temperate is slow
> enough that it sits in the pre heat temperature range long enough to
> evaporate the solvents out of the paste.

   That is what I thought. The problem is that it gets too dependent on the
oven thermal characteristics and on the boards you make. With the setup I am
using today I have more than 10 board models all manufactured in the same
oven without any changes in the setup and they range from very small to
almost the size of the oven !

> The problem I had is that there are only about 11 words left in the PICF84
> memory. My next job is to replace it with a PICF628, doubling the memory.
> That way I can program the ramp in.

   A bigger processor would be that way to go. Without the ramps the design
depends too much on the oven and boards being used.

> Alternatively, once the temp reaches the preheat value pressing the
> start/stop will turn off the heaters, pressing it again will turn them
back
> on to continue heating.

   I am using a 6 steps profile ! Not just preheating and soldering. Your
setup works, as long as you do not change the board sizes and densities too
much. With the ramps you can get a bigger variety of boards with the same
consistent results.

> I'm very interested in a continuos machine. I'm sure the continuous
toasting
> machines could be adapted. The small commercial belt machines have a bay
> with the preheat heater elements, the belt then moves the board to the
> soldering bay with the big heaters. The length of the bays need to be the
> correct ratio to ensure the board is in the bay for the appropriate time.

   I would not try that myself :-) If you have the need for bigger
productions that require a continous soldering system you have the money to
buy a comercial reflow oven ;-) There are many more problems to be dealt
with and unless you are trying to make a oven to sell as a product it will
cost you more in time than buying a ready made one. The main advantage on
the toaster oven idea is to get prototypes and small productions cheap and
as reliable as the ones made on bigger machines. You loose that advantage
completely oon bigger production runs ! I use the small oven for my short
runs and have the boards made for me when production is big.

Best regards,
Alexandre Guimaraes

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2002\12\11@124521 by Peter L. Peres

picon face
Just buy a desktop bun/biscuit oven and go with it. It is multizone etc.,
belt, everything.

Or pick up a proper desktop SMD oven on ebay. There was one about a year
ago for $300  or so.

Peter

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