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PICList Thread
'[EE] DIY Reflow Soldering'
2009\03\26@160618 by solarwind

picon face
I recently read an article on the Sparkfun website regarding reflow
soldering for surface mount components that can be done at home on any
form of hot plate (stove top frying pan, skillet, etc...).

I have several questions regarding this (that were unanswered in the
article, and for which I was unable to find answers on the Internet).

* I thought heat damages components. I was consistently cautioned not
to overheat components during hand soldering. If the idea is to heat
up the solder just enough to melt (and maybe a bit more so as not to
form a "cold soldered" joint), then wouldn't reflow soldering do the
same damage to components?

* One of my DIP chips came with a notice saying that it should be
"cooked" at 125 degrees Celsius prior to reflow soldering. I would
never reflow solder a DIP chip, but this is interesting. Why do they
have such requirements? Is it because of any possibility of trapped
moisture in the chip that could rapidly expand in high heat and damage
internals? What's the worst case for not obeying this notice?

* I've also heard of reflow soldering "profiles". What exactly are
these profiles? Is it a requirement that I adhere to them for homebrew
reflow soldering projects?

* How do I apply solder paste on pads? Do I just squeeze it out of the
tube and rub it consistently over the pads so that all of it is
connected? Does a very precise amount need to be applied discretely on
each individual pad? How is this done?

* Where to buy solder paste, are there different types, what brand,
what type? Should I use flux? Should I pre-flux the pads or apply flux
and then solder paste?

* I've also heard that it is wise to calibrate or know where your
skillet/stove reaches a certain temperature. What temperature is good
for reflow soldering? How do I measure this temperature?

* How long should the PCB be on the skillet/frying pan during the
reflow soldering process?

I know these are a lot of questions, but I am very interested in this
cost-effective do-it-yourself technique to solder surface mount and
fine pitch components on PCBs with ease.

--
solarwind

2009\03\26@162626 by Vitaliy

flavicon
face
solarwind wrote:
>I recently read an article on the Sparkfun website regarding reflow
> soldering for surface mount components that can be done at home on any
> form of hot plate (stove top frying pan, skillet, etc...).
>
> I have several questions regarding this (that were unanswered in the
> article, and for which I was unable to find answers on the Internet).
>
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?

No, unless the temperature is too high.


> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals?

Correct.


> What's the worst case for not obeying this notice?

Silicon popcorn. But in most cases, nothing bad will happen.


> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles? Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?

Profile is basically a temp vs time graph, that shows you what the
temperature should be at a certain point in time. What it boils down to, is
you need to preheat the board at a lower temperature (preheat), then quickly
raise the temperature so the solder paste melts (ramp-up), then cool the
board, but not too quickly (ramp-down).

A quick giggle brought this up (see graph on page 3):
http://www.actel.com/documents/Solder_Reflow_LeadFree.pdf

Notice that this is for lead-free solder.


> * How do I apply solder paste on pads? Do I just squeeze it out of the
> tube and rub it consistently over the pads so that all of it is
> connected? Does a very precise amount need to be applied discretely on
> each individual pad? How is this done?

Take a small cyringe, carefully file off the sharp end to make the end flat,
then use it to dispense solder paste. See this page for info on application
techniques:

http://www.seattlerobotics.org/encoder/200006/oven_art.htm

You don't need to be too precise, you just need to dispense the right
amount. Reflowing is self-correcting, to a point.


> * Where to buy solder paste, are there different types, what brand,
> what type? Should I use flux? Should I pre-flux the pads or apply flux
> and then solder paste?

This is the hard part. :)


> * I've also heard that it is wise to calibrate or know where your
> skillet/stove reaches a certain temperature. What temperature is good
> for reflow soldering? How do I measure this temperature?

See graph; you can wing it, or use a thermocouple.

The temperature isn't that critical for hobby stuff. Preheat the
oven/skillet, then quickly raise the temperature and wait until all the
solder paste melts.


> * How long should the PCB be on the skillet/frying pan during the
> reflow soldering process?

See graph.


> I know these are a lot of questions, but I am very interested in this
> cost-effective do-it-yourself technique to solder surface mount and
> fine pitch components on PCBs with ease.

You're on the right track. Baking is way easier than using a soldering iron,
or a heat gun.

Vitaliy

2009\03\26@163351 by Mark Rages

face picon face
On Thu, Mar 26, 2009 at 3:06 PM, solarwind <spam_OUTx.solarwind.xTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

Short answers cause I'm busy today:

Solder paste:
http://www.dealextreme.com/details.dx/sku.7952

Kapton stencil:
http://ohararp.com/Stencils.html

(you can buy better solder and better stencils, but these work).

Toaster oven:
http://www.goodwill.org

Profile:
bake on "broil" until the solder melts, then open the door until it
freezes again.

Overall:  this method isn't worth the trouble and mess for single
boards, and isn't economic for large quantities (>50 boards).  For
just a few boards, it works fine.  It turns out that most components
aren't super-sensitive to heat.  Connectors, etc. made with plastic
are the most susceptible.

Solder paste is more dangerous than solder wire: it would be easy to
get some on your hand (it's sticky) and then ingest it.

Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam@spam@midwesttelecine.com

2009\03\26@163451 by Herbert Graf

flavicon
face
On Thu, 2009-03-26 at 15:06 -0500, solarwind wrote:
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?

Almost all components are DESIGNED for reflow, so no, they won't be
damaged by it, assuming you follow a recommended profile.

> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals? What's the worst case for not obeying this notice?

Bingo. Think of a kernel of popcorn. Heat it up, it explodes. Same with
a chip. If you don't dry it out by "cooking" it, it will rupture during
reflow. The main issue is the damage may not even be apparent, very hard
to debug issues could result.

> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles? Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?

There are established profiles out there for reflow. Google should help
you there.

> * How do I apply solder paste on pads? Do I just squeeze it out of the
> tube and rub it consistently over the pads so that all of it is
> connected? Does a very precise amount need to be applied discretely on
> each individual pad? How is this done?

The pros have a mask and basically use a silk screen technique to get
the past on the board. While much more time consuming, simply squeezing
the paste on the pads will work pretty much just as well. Don't use
alot, experience will tell you how much. If you use to much chances are
either the joint will be rubbish, or you'll get a sometimes very had to
see bridge.

> * I've also heard that it is wise to calibrate or know where your
> skillet/stove reaches a certain temperature. What temperature is good
> for reflow soldering?

The temp alone isn't enough, you have to follow a reflow profile, which
details what temps to stay at for how long, and how quickly to get to
each temp. Google is your friend.

> How do I measure this temperature?

A thermometer? I'd use an IR one in a pinch.

> * How long should the PCB be on the skillet/frying pan during the
> reflow soldering process?

See above.

TTYL

2009\03\26@165239 by olin piclist

face picon face
solarwind wrote:
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?

It can, which is why there are such things as soldering temperature profiles
(temperature as a function of time).  Professional reflow equipment is not
cheap since it implements these profiles, ususally by moving the board thru
a series of "zones" at preset temperatures.

> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals?

Yes.

> What's the worst case for not obeying this notice?

Popcorn.

> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles?

Temperature as a function of time.  They are designed to get the solder to
flow with minimal heat stress to the components.

> Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?

Only if you want the parts to live.  There is some wiggle room to be sure,
but the more you deviate, the higher the probability of dead parts.

> * How do I apply solder paste on pads?

In real production, this is done with a stencil.  The stencil is usually
thin steel of a specific thickness.  The solder paste is sortof squeegied
accross the stencil so that it gets wiped off the stencil but blobs remain
in the voids formed by the holes in the stencil.  The stencil is then lifted
off the board and just the blobs of solder paste remain.

For one-off home use, you'd probably apply the paste manually with a
syringe, and then expect to fix a few shorts afterwards.

> * Where to buy solder paste,

Buying small quantities is tricky.  It also has a limited shelf life.

For one-off home construction, you are probably better off just using
regular solder and a fine tip iron for fine pitch parts.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\03\26@172401 by Joseph Bento

face
flavicon
face

On Mar 26, 2009, at 2:06 PM, solarwind wrote:

> I recently read an article on the Sparkfun website regarding reflow
> soldering for surface mount components that can be done at home on any
> form of hot plate (stove top frying pan, skillet, etc...).

Yes.  Even a toaster oven can be made to work for SMT soldering.  A  
convection oven with internal fan is preferable for better heat  
distribution. While a hotplate will work, most boards I've encountered  
are not perfectly flat, thereby greatly affecting the heat transfer.

> I have several questions regarding this (that were unanswered in the
> article, and for which I was unable to find answers on the Internet).
>
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?

Yes, heat damages components.  It's the way the heat is applied,  
however.  A solder iron may have a tip temperature of over 400c.  At  
this temperature, you need to complete your connection quickly or else  
rish damaging the component.  If you use an oven with paste solder for  
SMT components, you will typically limit the temperature to around  
200c.  Paste solder turns liquid at around 170c.   I have hand  
assembled many boards with SMT components and have never seen a  
component damaged in a 200c oven.

In my job (that was recently eliminated) we used a standard convection  
oven.  On the food tray, we placed a 1/4" thick aluminum sheet - quite  
substantial.  This sheet had a small hole drilled in a corner to allow  
placement of a K-type thermistor to monitor temperature.  Do not trust  
the dial setting on the oven.  The aluminum sheet was allowed to  
preheat to around 100c, where we would then place the board to be  
soldered.  Paste and components have obviously already been placed on  
the board.  Temperature would then be monitored on the aluminum plate  
till 200c is reached.  The oven would then be turned off, but leave  
the door closed to maintain the heat.  Watch your board around the  
most substantial sized components - inductors, power regulators, etc.  
Once the solder liquifies, open the oven door and allow plate and  
board to cool.   You'll happily find that there is very little touchup  
work required.

We used this method with .4mm pitch chips and resistors as small as  
0402.  It works surprisingly well, and for a small shop that can't  
afford SMD ovens, it is perfectly adequate.

>
> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals? What's the worst case for not obeying this notice?

If you're hand soldering the components, don't worry.  It is exactly  
because of trapped moisture that can otherwise affect the quality of  
the soldering.  When flowed, it is possible for the joint to  
crystalize if the moisture content is too high.

> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles? Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?

Don't worry for homebrew.  A profile is an EXACT temperature control  
for an EXACT period of time.  A SMD oven may heat the bottom of the  
board at 140c for 30 seconds while heating the top side to 200c within  
the same period.  This may be the specification to perfectly solder  
the part on a particular grade of PCB, where the temp would then be  
reduced in precise increments.

> * How do I apply solder paste on pads? Do I just squeeze it out of the
> tube and rub it consistently over the pads so that all of it is
> connected? Does a very precise amount need to be applied discretely on
> each individual pad? How is this done?

If you are placing SMD parts by hand, the solder is applied via a  
blunt hypodermic needle.  There are several sizes depending on the  
pitch of component you are working with, affecting the flow out of the  
needle.  Typically, the dispenser is the paste solder, and the needle  
screws right on the end.  There is a air operated foot pedal to  
pressurize the dispenser, allowing the solder to flow.

It can be done with a plunger applicator as well.  When doing an IC,  
it is not necessary to exactly apply the paste to each pad.  You can  
draw a small bead across the length of the pads, place the chip, and  
through practice, you will slide your soldering iron across the pads  
and perfectly soldering your component.  You can also use a hot air  
machine if you have access to one.

> * Where to buy solder paste, are there different types, what brand,
> what type? Should I use flux? Should I pre-flux the pads or apply flux
> and then solder paste?

I just buy the past from DigiKey.  It isn't cheap, and be advised they  
must ship it overnight since storage requires it be refrigerated.  
Kestler is typically the brand, and it is typically 63/37 not unlike  
wire solder.  The paste contains a no-clean flux, and if you bake your  
board in an oven, you may be surprised at how clean the board looks  
(no flux deposits) when done.  If you hand solder with paste solder,  
you'll likely need to clean up with some isopropyl alcohol.

>
> * I've also heard that it is wise to calibrate or know where your
> skillet/stove reaches a certain temperature. What temperature is good
> for reflow soldering? How do I measure this temperature?

That's where the thermistor comes in.  200c was where we would  
typically find very good results.

>
> * How long should the PCB be on the skillet/frying pan during the
> reflow soldering process?

At your adjusted temperature - ie 200c - till it melts.  
Unfortunately, since we are not talking about thousands of dollars  
worth of equipment, that is about the best answer.  200c will not  
typically damage your parts.  My experience is about 3 minutes from  
the time the board is placed on that aluminum sheet.  Most generic SMD  
parts are very inexpensive.  If you can afford to practice on a PCB,  
you'll gain a lot of confidence.  It actually is pretty easy once  
you've done it a few times.

>
> I know these are a lot of questions, but I am very interested in this
> cost-effective do-it-yourself technique to solder surface mount and
> fine pitch components on PCBs with ease.
>

It really does work.  Applying the paste and a steady hand with  
tweezers to place the parts may be the most difficult step.

Joe

2009\03\26@174757 by solarwind

picon face
On Thu, Mar 26, 2009 at 5:08 PM, Joseph Bento <josephspamKILLspamkirtland.com> wrote:
>
> Yes.  Even a toaster oven can be made to work for SMT soldering.  A
> convection oven with internal fan is preferable for better heat
> distribution. While a hotplate will work, most boards I've encountered
> are not perfectly flat, thereby greatly affecting the heat transfer.

* I heard that oil helps to evenly disperse heat. Also, some dude put
an aluminum block on his pan to distribute heat from the element.

* Also, do you recommend closed ovens or open type frying pans/skillets/etc?

> Yes, heat damages components.  It's the way the heat is applied,
> however.  A solder iron may have a tip temperature of over 400c.  At
> this temperature, you need to complete your connection quickly or else
> rish damaging the component.  If you use an oven with paste solder for
> SMT components, you will typically limit the temperature to around
> 200c.  Paste solder turns liquid at around 170c.   I have hand
> assembled many boards with SMT components and have never seen a
> component damaged in a 200c oven.

Thanks. I'll try and make something using my old oven that hasn't been
used in 10 years. It's really solid (but old), heats up quick and very
hot.

> We used this method with .4mm pitch chips and resistors as small as
> 0402.  It works surprisingly well, and for a small shop that can't
> afford SMD ovens, it is perfectly adequate.

This is heartwarming to know. I just might buy all surface mount
components from now on since the soldering part should be easy and I
already asked a million questions about making PCBs, so that should be
good too.

> If you're hand soldering the components, don't worry.  It is exactly
> because of trapped moisture that can otherwise affect the quality of
> the soldering.  When flowed, it is possible for the joint to
> crystalize if the moisture content is too high.

If the components I purchased/sampled did NOT come with a flashy
sticker telling me to pre-cook the chip before reflow soldering, do I
HAVE to cook it or can I go straight to the reflow soldering? I think
my parents would kill me if I left an oven on for 24 hours...

{Quote hidden}

Is the solder paste really toxic? I think it should be ok if I use
some medical-purpose gloves, no?

> It really does work.  Applying the paste and a steady hand with
> tweezers to place the parts may be the most difficult step.

All in all, do you (to everyone) recommend reflow soldering or normal
hand soldering? Is homebrew reflow soldering worthwhile, in your
opinion?

And solder paste seems to be expensive...

2009\03\26@181807 by cdb

flavicon
face


:: One of my DIP chips came with a notice saying that it should be
:: "cooked" at 125 degrees Celsius prior to reflow soldering

this shouldn't be a problem for a hobby, non commercial item. Where I
once worked - some baking would take 24 hours and included baking flex
pcb's as well. - I've used Ds1337 which come with a bake before you
use - and a nice pink (well it was blue to start with) age disk - for
proof of concept and one off hobby stuff I wouldn't bother -
commercial and medical equipmen

:: How do I apply solder paste on pads?t most definitely.

As others have said a small syringe - there are different size
hyperdermics and you need to get one that is large enough to only have
to apply slight pressure to move the solder paste otherwise add a air
pump with foot switch to your list-.


:: Should I use flux? Should I pre-flux the pads or apply flux
:: and then solder paste?

Yes - make sure that you get the flux that goes with the brand of
solder you are using -

Solder paste is the most carcianogenic form of solder as it is small
balls of solder combined in a wetting agent. It will feel and look a
bit like graphite paste, being small it can be absorbed by the skin.

Surgical/medical/household disposable gloves will be fine. Make sure
that you wear clothes that you won't use for anything else or wash the
clothes afterwards as solder paste can get EVERYWHERE surprisingly.

Solder pastes should eb kept in a fridge - not a fridge used for food
due to contamination. The paste from a fridge will need upt o 4 hours
to get to working temperature. Again though as you are not producing
medical or military goods you probably don't need to worry about the
fridge bit, the solder just won't last as long.  

Music to your ears - find a local board/manufacturing company, if they
make medical equipment they will probably have whole buckets of solder
they can't use anymore, which they are often willing to either give
away or for a small consideration - the solder will probably be
'dirty' and may have flux already mixed into it.

Colin
--
cdb, .....colinKILLspamspam.....btech-online.co.uk on 27/03/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







2009\03\26@182618 by Rolf

face picon face
Olin Lathrop wrote:
> solarwind wrote:
>  
>> * I thought heat damages components. I was consistently cautioned not
>> to overheat components during hand soldering. If the idea is to heat
>> up the solder just enough to melt (and maybe a bit more so as not to
>> form a "cold soldered" joint), then wouldn't reflow soldering do the
>> same damage to components?
>>    
>
>  

Who are you and what have you done with Olin?

Rolf

2009\03\26@183934 by Joseph Bento

face
flavicon
face

On Mar 26, 2009, at 3:46 PM, solarwind wrote:

>
> * Also, do you recommend closed ovens or open type frying pans/
> skillets/etc?

I don't think I'd use a skillet.  I've used a lab-grade hot plate such  
as might be used for heating a beaker and a common variety toaster /  
convection oven.  BTW NEVER use the oven for food once used for  
soldering.

>
> If the components I purchased/sampled did NOT come with a flashy
> sticker telling me to pre-cook the chip before reflow soldering, do I
> HAVE to cook it or can I go straight to the reflow soldering? I think
> my parents would kill me if I left an oven on for 24 hours...

Never done that myself.  Utah, where I live is exceptionally dry.  The  
humidity stickers that are in the bag with the desiccant pack usually  
stay around 10% - below the worry range that might require baking.

>
> Is the solder paste really toxic? I think it should be ok if I use
> some medical-purpose gloves, no?

Well, yes it is toxic since it contains lead.  There may be some other  
nasties in the paste as well.  Just wash your hands prior to eating /  
drinking / smoking, etc.  I've been playing with electronics since I  
was a kid, and there was a time when I'd use my teeth as a 'third  
hand' to hold the solder.  I don't do that any longer, but I don't  
take any special precautions other than washing my hands and ensuring  
good ventilation.

>
> All in all, do you (to everyone) recommend reflow soldering or normal
> hand soldering? Is homebrew reflow soldering worthwhile, in your
> opinion?
>

SMD soldering is tedious to solder with conventional tools and solder,  
though it is certainly possible.

> And solder paste seems to be expensive...

It certainly is.  (And wait till you try lead free!  A whole new game!)

For my hobby stuff, I still try to use through-hole components unless  
otherwise unavailable.

Joe

2009\03\26@191929 by solarwind

picon face
Thank you to everyone for the time you have taken to write such
detailed replies to my noobish questions.

I have also found another tool which seems to be interesting and very
inexpensive: http://www.engadget.com/2006/03/07/how-to-make-a-surface-mount-soldering-iron/

Also, since solder paste is expensive and doesn't keep well, (how long
does it keep anyway? in the fridge, that is), would it work if I were
to pre-tin the pads on the PCB by putting solder already on it, then
using the above tool to literally melt the solder as I place the
component on the pad?

2009\03\26@193723 by Mark Rages

face picon face
On Thu, Mar 26, 2009 at 6:19 PM, solarwind <EraseMEx.solarwind.xspam_OUTspamTakeThisOuTgmail.com> wrote:
> Thank you to everyone for the time you have taken to write such
> detailed replies to my noobish questions.
>
> I have also found another tool which seems to be interesting and very
> inexpensive: http://www.engadget.com/2006/03/07/how-to-make-a-surface-mount-soldering-iron/
>
> Also, since solder paste is expensive and doesn't keep well, (how long
> does it keep anyway? in the fridge, that is), would it work if I were
> to pre-tin the pads on the PCB by putting solder already on it, then
> using the above tool to literally melt the solder as I place the
> component on the pad?

1) Learn SMT soldering with a normal iron first.  You will use it
much, much, more than paste soldering unless you are an PCB assembly
shop.

2) $3.36 is not expensive. http://www.dealextreme.com/details.dx/sku.7952

--
Mark Rages, Engineer
Midwest Telecine LLC
markragesspamspam_OUTmidwesttelecine.com

2009\03\26@194127 by Bob Blick

face
flavicon
face

On Thu, 26 Mar 2009 19:19:24 -0400, "solarwind"
<@spam@x.solarwind.xKILLspamspamgmail.com> said:

> Also, since solder paste is expensive and doesn't keep well, (how long
> does it keep anyway? in the fridge, that is)

I've never had a problem with small containers of it going bad. The
stuff I use is pre-fluxed, I could imagine it separating if it was a big
container. A little one ounce container will last you a long, long time.

By the way, a syringe doesn't work on really tiny pads, too much solder
gets applied. The smallest pitch I've done by hand is .5 mm, and what I
do is spread a very thin coating of solder paste on a mirror, then
scrape(like raking leaves, not shoveling) your chip or connector on it
to transfer a little onto the pins. Then rotate the part for the next
row of pins, and carefully put the part on the board.

Cheers,

Bob

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2009\03\26@203556 by Joseph Bento

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It would be interesting to hear from among this group of professionals  
just how many of you use a toaster oven or hot plate for SMD soldering.

I had learned the trick many years ago, and was amazed the first time  
an EE  showed me toaster oven soldering. I was previously under the  
assumption (like Solarwind, perhaps) that these components were  
exceptionally fragile, and took thousands of dollars worth of  
equipment to handle.

Now, even in job interviews, I'm not afraid to mention the toaster  
oven.  When touring other shops, I see just how common it is!

Joe

2009\03\26@211754 by Jesse Lackey

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Just another datapoint... my setup is:

4-element 1500W toaster oven with convection fan.  I get good results
with this.  I recommend spending a bit of $ for something good.  Mine is
a Delonghi referb from ebay for $50.

The temperature settings and thermometer display (if any) on the oven is
more than worthless, it may cause you to really overcook boards.  I
spent $30 at jameco for a cheap meter with thermocouple.  Much much better.

Parts are sturdier than you think.  Just don't be on the super hot for a
long time.

Haven't tried lead-free, and probably never will as long as leaded is
available.  Just doing minor rework on lead-free boards made at a CM
shows how much hassle it is.  Lead is great stuff.

Be mindful and wash your hands.
Goes without saying to never use the oven for anything but boards.

I keep the paste in a mini fridge in a tupperware container, and I keep
food in the fridge as well.  I don't see what the problem is, but I'm
also careful.

I use syringes as well as stencils to place the paste.  Syringes work
well but after awhile your hand starts hurting from having to maintain
pressure.

For both syringes and stencils, my problem remains solder bridges on
tssop packages.  0402 and soics and whatnot are almost always fine.

For cheaper stencils, get mylar at pololu.com.

I just got my first metal stencil ($99) and a $200 holder for stencils
at stencilsunlimited.com.  A big improvement, but I can tell I'm going
to get some tssop bridges on 3 boards I'm doing at this very moment, and
aligning the stencil to the board remains a pain.

Once you start down this road, I recommend a hot air SMT rework station,
it is great if ICs wind up being askew, you can just heat them and
remove cleanly.  I got mine for $150-ish at circuitspecialists.com.
Highly recommended.  You can place parts faster and be less
fussy/worried when you know you can just pull them if there is a problem.

My "reflow profile":
heat to 100deg C for a minute or two, to get everything relatively
evenly warm.
then heat to 200deg C or so over a minute or so; watch the solder paste,
it will melt in a slow wave, usually back to front of the oven.
when the paste in the front has melted, I usually let it go up another
5-10deg over 10 seconds.
then I turn off oven, crack the door an inch, and wait for cooldown.

Works pretty well all told.
Have a magnifier and I suggest really skinny solder braid - I have some
0.025" stuff, mg chemicals #423 from digikey.  Recommended.

If you have big metal parts (like a large inductor) the paste for it is
what you should watch, it will melt last, and the warmup and 200deg C
times may take longer because of its thermal mass.  Or: don't try to do
it in the oven, just do it by hand later.  I haven't yet had a problem
but a friend did.

And there you have it, a summary of a fair amount of experimentation.

Improving things to get tssop paste to be the right amount consistently
and without a lot of fiddling of the stencil is the next important step.
 I may spring for a kilobuck+ stencil holder system to solve this, some
research is necessary here.

BTW, I'm making three boards with ~400 SMT parts on each right now, and
have no real concern about the baking process or damage.  There's 12
tssops and approx $400 in parts on each.  You just have to really
inspect the tssops and use current limited power supplies for the
power-up moment.

Good luck, it is fun but sometimes tedious...
J



solarwind wrote:
{Quote hidden}

2009\03\26@213648 by Jesse Lackey

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Just a little addendum...

If curious, the boards I'm doing are the 3rd, and really hopefully
final, proto of:
http://www.celestialaudio.com/4ch/index.html
the one pictured was done by hand with a soldering iron, since it was
before I got going with the toaster oven.

I got my paste from techni-tool.com
kester R276, bought 3 syringes, almost out, lasted a year and did quite
a few boards with it.  p/n 488SO540
I also got two needles: 272PR021 and 272PR939.  I use the larger one a
lot, the smaller rarely.
the plunger for the syringe came from digikey: KE1505-ND.

I would recommend getting the larger needle of the above and something
even bigger to make it easier to put paste down on largeish pads.  But
not really needed.

J






Jesse Lackey wrote:
{Quote hidden}

2009\03\26@213800 by solarwind

picon face
By the way, I'm going to quote some of you (with credit) on my blog. I
don't make money off of it and it's purely a hobby blog so I hope you
all don't mind. If you object, please let me know immediately.

2009\03\26@220311 by Joseph Bento

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On Mar 26, 2009, at 7:37 PM, solarwind wrote:

> By the way, I'm going to quote some of you (with credit) on my blog. I
> don't make money off of it and it's purely a hobby blog so I hope you
> all don't mind. If you object, please let me know immediately.

Just give us the URL where we can find it.  :-)

Joe

2009\03\26@221311 by Jesse Lackey

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I don't mind at all, for any postings I make.  A link to my homepage is
appreciated but not required.

BTW, once you get the toaster oven and whatnot going, you start wishing
you had a pick & place machine.  That is a whole nuther adventure, but
for the amusement of PIClist people, I bought one of these:

http://www.bidservice.com/Browses/DHTML_PHOTOS.ASP?ProductID=13148&Mfg=MRSI&Mdl=501&InvNum=30063

Was $200K new in 1991, and I believe it can pick&place 0201 sized parts.
 DOS software originally on an AT 286 rackmount.  That is pretty good
vision recognition folks, 3 cameras, on a 16mhz? 286.

Got it a year ago off ebay for approx a penny on the dollar of its
original price, and had it shipped from ohio to california, where it
sits in my shop waiting to be essentially completely reprogrammed with
code that I'd largely have to write.

If anyone in the bay area would like to check it out / do that
reprogramming work (um...for free or nearly so), let me know.  :)  You
get it workable smoothly from Eagle pick&place data, and you can use it
whenever you'd like, forever.

Ever ambitious to the border of unreasonable,
J




solarwind wrote:
> By the way, I'm going to quote some of you (with credit) on my blog. I
> don't make money off of it and it's purely a hobby blog so I hope you
> all don't mind. If you object, please let me know immediately.

2009\03\26@230347 by solarwind

picon face
Ok, here's a link to my blog post with all the information you guys
have provided, as well as some research that I have done myself.
Thanks again to all!

solar-blogg.blogspot.com/2009/03/diy-reflow-soldering.html

2009\03\26@232325 by Joseph Bento

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On Mar 26, 2009, at 8:13 PM, Jesse Lackey wrote:

>
> If anyone in the bay area would like to check it out / do that
> reprogramming work (um...for free or nearly so), let me know.  :)  You
> get it workable smoothly from Eagle pick&place data, and you can use  
> it
> whenever you'd like, forever.

Wouldn't that be something.  Use a pick-n-place machine to populate  
your board, and solder it in a toaster oven!  :-)

Joe

2009\03\26@232730 by cdb

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:: have also found another tool

Have you looked up the protoyping PCB company that produces a special
presoldered board for SMD components?

As their advert says a 5 year old who can use a soldering iron can use
the board.

I'm trying to think of their name - schtick or something - they're in
the US.

Colin

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2009\03\26@235826 by solarwind

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On Fri, Mar 27, 2009 at 3:27 AM, cdb <RemoveMEcolinTakeThisOuTspambtech-online.co.uk> wrote:
> Have you looked up the protoyping PCB company that produces a special
> presoldered board for SMD components?
>
> As their advert says a 5 year old who can use a soldering iron can use
> the board.
>
> I'm trying to think of their name - schtick or something - they're in
> the US.

I can't find it, but this would definately be interesting. How would
one go about soldering the components if they use this board?

2009\03\27@004656 by Bob Blick

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cdb wrote:
>
> Have you looked up the protoyping PCB company that produces a special
> presoldered board for SMD components?
>
> As their advert says a 5 year old who can use a soldering iron can use
> the board.
>
> I'm trying to think of their name - schtick or something - they're in
> the US.

http://www.schmartboard.com/

I've never tried them.

Cheers,

Bob


2009\03\27@014432 by solarwind

picon face
On Fri, Mar 27, 2009 at 4:46 AM, Bob Blick <spamBeGonebobblickspamBeGonespamftml.net> wrote:
> http://www.schmartboard.com/
>
> I've never tried them.

Oh, THAT's what you meant... This was the first thing I actually
considered. I thought you meant PCB company that produces your design
with pre soldered pads...

2009\03\27@051848 by Alan B. Pearce

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>> * One of my DIP chips came with a notice saying that it should be
>> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
>> never reflow solder a DIP chip, but this is interesting. Why do they
>> have such requirements? Is it because of any possibility of trapped
>> moisture in the chip that could rapidly expand in high heat and damage
>> internals?
>
>Correct.

Agreed.

SMD chips come with similar instructions, and will come in hermetically
sealed packaging which has been vacuum packed with silica gel to prevent
moisture ingress into the chips. The couple of packages I have seem to be
certified for 6 months if the sealing isn't broken.

The 125C does sound rather high though. I know our PCBs for space flight are
required to be ovened for a few hours at 50C (typically left in oven
overnight), for similar reasons, to prevent measling when soldering.

2009\03\27@071104 by olin piclist

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Joseph Bento wrote:
> A solder iron may have a tip temperature of over 400c.

That's 750F.  Maybe that's true for the old fashioned fixed wattage irons,
but 750F is way too high for normal soldering.  I use 600F for normal use
and sometimes crank it to 650F or 700F for special circumstances or
desoldering.


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