I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?

On 10/02/2015 09:04, mike wrote:
I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?

Can you make up a very small TC and push it into the ball grid of a
scrapper and monitor with different settings of heat /airflow/
hotplate-temp ?

On 10/02/2015 15:48, N_Cook wrote:
On 10/02/2015 09:04, mike wrote:
I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?

Can you make up a very small TC and push it into the ball grid of a
scrapper and monitor with different settings of heat /airflow/
hotplate-temp ?

totally OT, bloody thunderbird, where did the italicised "airflow" come
from in my previous

On Tuesday, February 10, 2015 at 1:04:36 AM UTC-8, mike wrote:
I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?


This might help.

http://www.instructables.com/id/Toas...Soldering-BGA/

On 2/10/2015 7:48 AM, N_Cook wrote:
On 10/02/2015 09:04, mike wrote:
I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?

Can you make up a very small TC and push it into the ball grid of a
scrapper and monitor with different settings of heat /airflow/
hotplate-temp ?
Surely I can.
I could also build a flux capacitor out of a tin can and some wings
off a gnat.

The whole idea of asking a question is to leverage the work of others.

In particular, what air temperatures are people using successfully?
That's the easiest parameter to control, but I'm open to options.

On 2/10/2015 8:17 AM, wrote:
On Tuesday, February 10, 2015 at 1:04:36 AM UTC-8, mike wrote:
I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?


This might help.

http://www.instructables.com/id/Toas...Soldering-BGA/

Nope.
The web is full of instructions written by people who have no idea
what they're doing with zero specificity for reproduction of their work.
Just because ten people took a butane torch to their GPU doesn't mean
I want to try it. There's one video that made a great production
out of heating the WRONG chip.

The whole concept of reflowing without reballing is a crap shoot.
I don't know a lot about it, that's why I'm asking questions,
but,
when your balls are fractured, you need ALL the balls melted at the same
time on BOTH sides of the fracture and maybe some vibration to make
the crack close so surface tension can mend the fracture.

Doing that without breaking something else is gonna require
some precise temperature control.

The other end of the spectrum is videos showing jigging the board
in a commercial reflow machine and pressing "go". Still no specificity
on what temperatures are being measured or what the air temperature
driving it might be.

I have a hot air gun with digital temperature readout with one degree
resolution. They can't be measuring anything but the air temperature.
What we want to know is the temperature of the workpiece.
Given that air temperature is the only parameter it can control,
the needed info is what AIR temperature should we be using as we
measure the workpiece with other tools.

The thermal profiles are well known. It's the process of getting there
that's not obvious.

I'm interested in the physics and thermodynamics of the process.

N_Cook skrev:
On 10/02/2015 15:48, N_Cook wrote:


Can you make up a very small TC and push it into the ball grid of a
scrapper and monitor with different settings of heat /airflow/
hotplate-temp ?

totally OT, bloody thunderbird, where did the italicised "airflow" come from
in my previous

Formatting.
Slashes around something put something in /italics/
Asterisks around something makes something *bold*
Underlines around something _underlines_ it.

Leif

--
Je suis Charlie

On 2015-02-10 10:04:23 +0100, mike said:

I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?
I have heat guns with open loop variable power input.
And some with thermal feedback to control the air temperature.

I'm using thermocouples on top and bottom of the board
and manually controlling heaters while watching temperatures.
None of the heat sources are currently set up for computer control.

I'd like to try fixed heater positions and control the heater power
for better repeatability.

First thing that comes to mind is to have the air temperature
track the board temperature with the difference set to get the
proper temperature ramp at the chip. Then there's the relationship
between air flow rate and air temperature.

That should minimize
overheating. This has the potential to bloom into a local
microcontroller and a computer interface and graphs and and and...

Or, am I worrying too much and should just use fixed temperature
air.

What temperature air?

I've used a 200°C bottom heater and a 300°C top heater on a YIHUA 853AA station
for nvidia chips (some ATI too) reflows on laptops (mainly mac laptops)

10 minutes letting the heat stabilize on the board, then 3 minutes with
7 on air flow control
then stop everything and let cool the board.
I don"t desoldier the chip, just reflow it (put some flux on the border
of the chip)

I have so far some 95% success on some 20 laptops.
I began this one year ago, the first ones are still working ...

good luck.

--

Jean-Yves.

On Tue, 10 Feb 2015 01:04:23 -0800, mike wrote:

I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?

Recommended by whom? Recommendations are all over the map. Here's
mine.

Much depends on the type of solder used for the BGA chips. My
guess(tm) is that most BGA's use solder balls which solder at 217C and
starts to reflow at about 200C Meanwhile, the rest of the board is
SnAgCu solder paste, which starts to melt at about 225C. These temps
are from my measurements, not from the solder manufacturers charts and
take into consideration my instrument inaccuracies. The trick is to
target the oven temperature between these two temperatures so that the
BGA balls reflow, but the components on the PCB are untouched.

Getting the temperature even across the board is a major problem. I've
made measurements with an IR thermometer and thermocouple probes which
convinced me that this was impossible. Therefore, protecting the PCB
with an aluminum foil shield might be a good idea.

In the past, I would use my cheapo SMT rework hot air gun for
reflowing BGA chips. It would work on the smaller BGA and flip chips,
but fail miserably on the larger chips. I gave up using it for BGA
repair.

Recently, I purchased a Black and Decker toaster oven at Kmart for
about $25 to do some experiments. I reflowed some old PCB's to test
the settings and thermal control. Things went well, so last week, I
reflowed 14 HP JetDirect cards and 4 HP printer formatter cards. Some
photos:
http://www.11junk.com/jeffl/pics/repair/BGA%20reflow/index.html
All 14 JetDirect cards worked, although it's too soon to determine if
the fix is permanent. Only one of the formatter cards didn't work.
Not a bad percentage for essentially an uncontrolled reflow.

During the above reflow test, I make quite a few changes to the
temperature, timing, protection, etc. What I settled on is:
10 minutes preheat to 215C without the board in the oven. When I open
the door and insert the board, the temperature drops quickly. I then
reset the temperature dial to 190C and bake for 8 to 10 minutes. At
the end I turned off the oven power, but did NOT open the oven door.
When the temperature drops to about 100C, I open the door, leaving the
boards still in the oven. About 3 minutes later, they are cold enough
to touch and are removed.

Not the best temperature curve possible, but it works. What makes it
work is that the thermal mass of the cheap junk oven is very small
compared to a proper oven with insulation, firebrick, and a proper
controller.

Much of my inspiration came from:
http://www.wayupnorth.ca/blog/2012/06/12/you-baked-what/
and various articles on:
http://www.FixYouOwnPrinter.com

Notice that I did not protect the PCB with aluminum foil. I did that
with some early board tests and found that it didn't do much except
protect some electrolytic capacitor jackets. (I did remove the
plastic front panels from the JetDirect cards). As long as the
temperature was kept below where the solder paste on the PCB reflows,
there were no problems. None of the other key factors seemed to be
particularly critical. The bake time was varied from 5 minutes to 15
minutes. Anything over 7 minutes at 190C seemed to work.

Also notice that I didn't use flux. I'm fairly sure some really fluid
flux would have helped, but I didn't have any handy and didn't have
time to make some. When I previously tested the use of flux, I found
that the alcohol base had evaporated long before the solder balls had
begun to reflow. In other words, the flux didn't do anything. I did
as well using just alcohol and no flux which just cleaned the BGA from
accumulated dust and grease.

Several authors have suggested putting a weight on the BGA to help
push the broken connections together. That proved to be a problem.
The added thermal mass of the weight caused the heat distribution
across the BGA chip to change, which probably resulting in good reflow
around the edges of the BGA chip, and lousy reflow near the middle. At
least that's my guess why a weight made things worse.

Whether all this will work for motherboards has yet to be determined.
I'm not even sure they'll fit in my toaster oven. I have about 5
candidate laptops waiting, but the PCB's are still in the laptops. It
will take time to extract and retest them. Probably next month.

Good luck.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2/12/2015 9:25 AM, Jeff Liebermann wrote:
On Tue, 10 Feb 2015 01:04:23 -0800, mike wrote:

I've got another laptop needing a nVidia chip reflow.
I'm refining the technique.
What's the recommended air temperature?

Recommended by whom? Recommendations are all over the map. Here's
mine.

Much depends on the type of solder used for the BGA chips. My
guess(tm) is that most BGA's use solder balls which solder at 217C and
starts to reflow at about 200C Meanwhile, the rest of the board is
SnAgCu solder paste, which starts to melt at about 225C. These temps
are from my measurements, not from the solder manufacturers charts and
take into consideration my instrument inaccuracies. The trick is to
target the oven temperature between these two temperatures so that the
BGA balls reflow, but the components on the PCB are untouched.

I suspected that one should use the lead-free profiles. ???

Getting the temperature even across the board is a major problem. I've
made measurements with an IR thermometer and thermocouple probes which
convinced me that this was impossible. Therefore, protecting the PCB
with an aluminum foil shield might be a good idea.

In the past, I would use my cheapo SMT rework hot air gun for
reflowing BGA chips. It would work on the smaller BGA and flip chips,
but fail miserably on the larger chips. I gave up using it for BGA
repair.

Recently, I purchased a Black and Decker toaster oven at Kmart for
about $25 to do some experiments. I reflowed some old PCB's to test
the settings and thermal control. Things went well, so last week, I
reflowed 14 HP JetDirect cards and 4 HP printer formatter cards. Some
photos:
http://www.11junk.com/jeffl/pics/repair/BGA%20reflow/index.html
All 14 JetDirect cards worked, although it's too soon to determine if
the fix is permanent. Only one of the formatter cards didn't work.
Not a bad percentage for essentially an uncontrolled reflow.

During the above reflow test, I make quite a few changes to the
temperature, timing, protection, etc. What I settled on is:
10 minutes preheat to 215C without the board in the oven. When I open
the door and insert the board, the temperature drops quickly. I then
reset the temperature dial to 190C and bake for 8 to 10 minutes. At
the end I turned off the oven power, but did NOT open the oven door.
When the temperature drops to about 100C, I open the door, leaving the
boards still in the oven. About 3 minutes later, they are cold enough
to touch and are removed.

Not the best temperature curve possible, but it works. What makes it
work is that the thermal mass of the cheap junk oven is very small
compared to a proper oven with insulation, firebrick, and a proper
controller.

I've been afraid to put a whole motherboard in a toaster oven, assuming
I could find one big enough. There's lots of plastic stuff/connectors
etc on the board.
Most toaster ovens have exposed elements. You get lots of infrared and
a variable amount of convection heating. That scares me too. Thought about
putting reflective foil everywhere but the chip and count on the IR to
do it. But it's completely uncontrolled.



Much of my inspiration came from:
http://www.wayupnorth.ca/blog/2012/06/12/you-baked-what/
and various articles on:
http://www.FixYouOwnPrinter.com

Notice that I did not protect the PCB with aluminum foil. I did that
with some early board tests and found that it didn't do much except
protect some electrolytic capacitor jackets. (I did remove the
plastic front panels from the JetDirect cards). As long as the
temperature was kept below where the solder paste on the PCB reflows,
there were no problems. None of the other key factors seemed to be
particularly critical. The bake time was varied from 5 minutes to 15
minutes. Anything over 7 minutes at 190C seemed to work.

Also notice that I didn't use flux. I'm fairly sure some really fluid
flux would have helped, but I didn't have any handy and didn't have
time to make some. When I previously tested the use of flux, I found
that the alcohol base had evaporated long before the solder balls had
begun to reflow. In other words, the flux didn't do anything. I did
as well using just alcohol and no flux which just cleaned the BGA from
accumulated dust and grease.

Several authors have suggested putting a weight on the BGA to help
push the broken connections together. That proved to be a problem.
The added thermal mass of the weight caused the heat distribution
across the BGA chip to change, which probably resulting in good reflow
around the edges of the BGA chip, and lousy reflow near the middle. At
least that's my guess why a weight made things worse.

Whether all this will work for motherboards has yet to be determined.
I'm not even sure they'll fit in my toaster oven. I have about 5
candidate laptops waiting, but the PCB's are still in the laptops. It
will take time to extract and retest them. Probably next month.

Good luck.

My current tooling consists of a bottom heater made from an old TIVO
case. I cut a 2"x2" hole in the top for the BGA chip area to sit on
and drilled a hole in the side for a power-controlled heat gun. Welded some
baffles inside to guide the air from the heat gun to the square hole.

I sit the board over the hole with thermocouples on the underside
and touching the BGA on the top. Aluminum foil protects the part of the
top that's not the BGA. Flux applied.

Top gets heated with a commercial SMT rework heat gun with precise air
temperature
control. My air compressor is running wide open and I'm taking all the
air flow I can get.

I know what package temperatures I want and have some idea from the
thermocouples.

What I don't know is what air temperature I should be using from the
heat guns.

Too low won't get it all hot enough.
Too high will burn something.

I was hoping to avoid a bunch of experiments to determine it
empirically. Would be nice to have a target temperature to start
from.

This site is interesting:
https://www.youtube.com/watch?v=c_Qt5CtUlqY

I hava a Maxtra 852D+ rework station.
It's capable of 550W, but the air flow isn't high enough
to keep the heater duty cycle high. I have very little
actual experience with the unit. And my thermocouples
read
the air temperature 30C lower than the digital readout.
Very small changes in position make radical differences in the
measured temperatures.

I seek less ambiguity ;-)

On Thu, 12 Feb 2015 15:51:48 -0800, mike wrote:

I suspected that one should use the lead-free profiles. ???

Yes, if the oven temp controller had the ability to follow a
temperature profile. I'm not even trying to do that. Buy
coincidence, just shoving in the board into a pre-heated oven, and
letting it cool down seems to follow somewhat of a reasonable ramp,
soak, and cool profile. However, that's pure luck, not intent. My
point is that for reflow (i.e. repair) it does not seem to be that
critical. Once I understood what was happening, I soon discovered
what was the causing most of the reflow failures:
- Too cold during soak.
- Too short a soak time.
Everyone was too worried about destroying parts by over heating, so
they went for the lowest possible temperature and the shortest
possible soak time. That's not going to work as I proved to myself by
trying some of those recommendations. What I found was that I could
soak for quite a long time as long as I didn't get close to the
melting point of the solder paste used to solder the non-BGA parts. If
I could keep the temperature at about 220C, I could leave the board in
the oven nearly forever and it would come out ok. However, there is a
problem. Because I didn't have a proper temperature controller, doing
that would cause the temperature to slowly climb. The result is that
the soak temperature is not constant but rather an increasing ramp. I
can live with that as long as I target the end of the ramp at less
than about 220C. If you want to do it right, go thee unto eBay and
spend about $70 on a programmable oven controller.

I've been afraid to put a whole motherboard in a toaster oven, assuming
I could find one big enough. There's lots of plastic stuff/connectors
etc on the board.

Presumably, you could find a sacrificial motherboard to test. Shove
it into the oven at the highest expected temperature for a reasonable
time and see what melts or burns. Thermoplastic parts will melt.
Thermosetting plastic parts will not. You'll find most connectors
made from thermosetting plastics because the original motherboards are
soldered in a IR oven, which uniformly heats everything to the same
temperature. However, if you want to be sure, LOOSLY wrap the
connectors in aluminum foil. You want some air gap between the foil
and the connector so that air acts as an insulator.

Most toaster ovens have exposed elements.

Really? It thought the UL banned that in the 1950's. My Black &
Decker has two glass tubes with heating elements inside.

You get lots of infrared and
a variable amount of convection heating.

I think you'll find that it's almost all IR with a tiny amount of red
in the visible spectrum from the red glow. Convection implied air
flow. Unless you buy a convection oven, the IR (heat) is very
unequally distributed around the oven. I proved that to myself when I
ran my thermocouple probe around the oven to see how bad it was. My
guess(tm) is about 40C from the hottest near the center to the coldest
near the lower corners.

That scares me too.

Note my domain name: LearnByDestroying.com
You haven't learned anything until you've destroyed it and then had to
make it work.

Thought about
putting reflective foil everywhere but the chip and count on the IR to
do it. But it's completely uncontrolled.

Yep, but as I found, it works well without the proper controls. Sure,
I would like an overpriced oven with the proper profiles, but lacking
the financial justification, I used what I had and it worked. Foil
works if leave an air gap.

My current tooling consists of a bottom heater made from an old TIVO
case. I cut a 2"x2" hole in the top for the BGA chip area to sit on
and drilled a hole in the side for a power-controlled heat gun. Welded some
baffles inside to guide the air from the heat gun to the square hole.

I'll make it simple for you. Hot air does not transfer enough heat by
convection. Close in, radiation is a far more efficient heat transfer
mechanism. Loose the hot air gun, hair dryer, or flame thrower, and
switch to something that resembles an IR source, such as a heater.

Top gets heated with a commercial SMT rework heat gun with precise air
temperature control.

Again, lose the hot air gun. I have one of those. It will work with
a nozzle that is made for the BGA chip. I only have one size (forgot
which one) and that works because *ALL* the hot air lands on the BGA
top. That's not the case with just blowing hot air in the direction
of the BGA. When I tired that, I found that it took me about 30
minutes to heat the BGA top to 220C. I could do the same with the
proper nozzle in about 20 minutes, or with an IR heater in about 10
minutes. (The times are from memory and may be off somewhat).

My air compressor is running wide open and I'm taking all the
air flow I can get.

Your air compressor is cooling the chip. Try the same wattage heater
with slow or fast air. You'll find that the final temperature of the
slow moving air is much higher than the fast air.

I know what package temperatures I want and have some idea from the
thermocouples.

What I don't know is what air temperature I should be using from the
heat guns.

It doesn't matter. Monitor the BGA case temperature and do whatever
it takes with the hot air gun to make it happen.

I was hoping to avoid a bunch of experiments to determine it
empirically.

Man did not discover how to use fire without someone getting their
fingers burned. I could work out the thermodynamic concepts, but with
your uncontrolled setup, it's unlikely to be achievable or
reproducible. It think you could forget about putting your finger in
the fire, but a thermometer or thermocouple would work nicely. One
measurement is worth a whole bunch of guessing.

Would be nice to have a target temperature to start
from.

I gave you that in my previous rant. Somewhere between where the BGA
solder reflows, and where the solder paste starts to soften. My
guess(tm) is between 200C and 225C.

This site is interesting:
https://www.youtube.com/watch?v=c_Qt5CtUlqY

Stencils and solder paste work very will with BGA chips. Good video,
but I wouldn't try that with a 400+ pad BGA chip.

I hava a Maxtra 852D+ rework station.

I have exactly the same soldering station, except it says SAIKE
instead of Maxtra. Not great, but good enough and the price was
right.

It's capable of 550W, but the air flow isn't high enough
to keep the heater duty cycle high. I have very little
actual experience with the unit. And my thermocouples
read
the air temperature 30C lower than the digital readout.
Very small changes in position make radical differences in the
measured temperatures.

Yep. The thermocouple running the display is near the nozzle end in
the hand piece. By the time the air has gone to the nozzle, it has
cooled down quite a bit.

I seek less ambiguity ;-)

There is no one answer because everyone's setup is radically
different. I just want to fix my backlog of dead boards and move on
to something more interesting. Good luck.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558