Yet another bulging-capacitors replacement

[Arfa Daily]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:Jo2dnfqSRvF9IOPRnZ2dnUVZ_sidnZ2d@earthlink.com...

Arfa Daily wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
news:m5ednfqzQtE_8ePRnZ2dnUVZ_qWdnZ2d@earthlink.com...
?
? Arfa Daily wrote:
??
?? Well Jim, that was why I used the word "potentially", but judging by
the
?? size of the pins used to couple the power supply's output into the
?? board -
?? if you've been following the thread, you will recall that I previously
?? described them as being of the size you would find on the line cord
for a
?? kettle - then I wouldn't say that there was too much in the way of
?? reserve.
?
? "The size you would find on the line cord for a kettle" doesn't have
? much meaning in the US.

Why is that ? You have electric kettles in your kitchens - I've used
them.


I've never seen one. Even Coffee pots are rare these days.


Or don't you call them kettles ?. OK, anyway, if it's a better
description,
the size of the round ground pin on a line cord that has a three pin
plug.
Is that more meaningful ? 3/16" diameter maybe ? 4mm ?


3/16" is between AWG 5 & AWG 4. 4 mm is between AWG 7 & AWG 6. How
much current do those kettles draw?


--

Typical UK kettle is 2 - 3kW so 8 to 12 amps or thereabouts. Now, I'm really
confused that you say that you've never seen one. How do you boil water for
a cup of tea, or a cup of instant coffee ? Whenever I come to Florida, I
stay in a private rental home, and although some have had a kettle that
heats from a ring on the cooker, I'm sure that I have also stayed in homes
that had an electric version. Or maybe I'm mistaken on this ? Perhaps with
your line power at only 110v at a non 3 phase outlet, the current levels are
impractical with an element powerful enough to heat the water in short
order. Here, every home - and I really mean *every home* - has one. It is a
known problem for the electricity grid controllers, when TV ads come on in
the middle of the popular soaps. Short term demand goes through the roof, as
everyone rushes out to make a cup of tea or coffee, at the same time. The
controllers genuinely have to know the advert schedules in the TV
programmes, and factor this into their load shedding operations.

Arfa

 

[Arfa Daily]

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news4vs76df7mcfo4o21nte5ok0l1b2g490bg@4ax.com...

On Wed, 1 Sep 2010 02:40:53 +0100, "Arfa Daily"
arfa.daily@ntlworld.com> wrote:

All of the processing power is in those two BGAs Jeff.
(...)

Thanks for the details. I really don't know anything about such
dedicated game machines. I just assumed that all such machines used
common processors to make development easier.

That's a LOT of processing power, needing a lot of amps to perform ...

I found the Kill-o-watt meter and stuffed it in line with my Dell
Optiplex 960 (E8500 3.2Ghz). 43 watts at idle, 70 watts max when
playing a DVD (not including LCD monitor). Speedfan 4.40 says 31C for
both CPU cores after about an hour. The one large fan is barely
spinning and very quiet (which is why I bought this one). When I set
the fan to run full speed, it's quite loud.

The fan on these things *is* large, as is the heatsinking assembly, and
when
the processor finally decides to ramp the fan up, it sounds like a vacuum
cleaner. For this reason, at idle they tend to run it at below what I
would
consider a 'sensible' minimum, exacerbating the thermal stresses on the
chips, their (lead-free) soldering, and the board to which they are
attached.

Well, theory suggests that the life of a semiconductor device is
greatly affected by the number of thermal cycles it experiences
(thermal fatigue). I don't know if this also applies to CPU's or
whatever is in those BGA chips (FPGA/GPU?), but might be something
else to worry about. I would guess(tm) that the large aluminum heat
sink would moderate any abrupt changes in temperature, thus making it
less of a concern. However, that might not be the case for the solder
balls supporting the BGA.



--
Jeff Liebermann jeffl@cruzio.com

The soldering under the BGAs letting go, is the commonest problem with both
the Sony PS3 ( "yellow light of death") and the X-Box 360 ("red ring of
death")

Those names for the conditions refer to the behaviour of the front panel
indicator LEDs when the faults that result, show themselves.

I am quite convinced that the slow running of the fan at idle, is a major
contributory factor in the failing of the BGA soldering.

Arfa

 

[Mike Tomlinson]

In article <BDDdo.2319$3p1.124@hurricane>, Arfa Daily
<arfa.daily@ntlworld.com> writes

Just as a matter of interest Meat, what is your preferred brand and type of
heatsink goop when working with these very high power processors?

I'd recommend Arctic Silver.

I have always
resisted using this stuff, because it's so messy, and so hard to remove
unless you use the complementary cleaner

nah, standard IPA works fine. The trick is to use clean tissue wetted
with IPA, wiping just once or twice then replacing with a fresh piece,
repeating until the CPU is clean. If you go back with used tissue, you
just spread the AS about more.

If it makes that much mess, you're using too much. See the application
tips on the AS website. You literally only need a half-a-grain-of-rice
sized blob in the centre of the CPU heat spreader, it'll spread out by
itself with pressure from the heatsink. Note AS say it can take a few
heat/cool cycles to become fully effective, and indeed this is what I
have found.

, but if it really is that much more
effective

It is. A colleague at work was struggling to cool a CCD (a big one!)
without having to resort to cryogenic cooling. He was experimenting
with a Peltier cooler and unable to transfer heat away from the CCD fast
enough. I suggested he try replacing the standard white goop with AS
and he was astonished at the massive improvement in heat transfer.

--
(\__/)
(='.'=)
(")_(")

 

[Mike Tomlinson]

In article <ebug76lk13plippid57h6q6vacu8ve4om9@4ax.com>, Jeff Liebermann
<jeffl@cruzio.com> writes

I don't believe it. The winner of the power hogging consumer CPU
contest was the DEC/Intel Alpha 21364 (EV79):

I herded a fleet of 21264s (AlphaServer DS10) for a while. Impressive
heatsinks in those. One is still in use today.

--
(\__/)
(='.'=)
(")_(")

 

[Mike Tomlinson]

In article <mzvfo.28576$zA5.13324@newsfe16.ams2>, Arfa Daily
<arfa.daily@ntlworld.com> writes

Why is that ? You have electric kettles in your kitchens - I've used them.

They do, they just take three times longer to boil. They're nowhere
near as ubiquitous in American kitchens as they are in the UK.

--
(\__/)
(='.'=)
(")_(")

 

[Mike Tomlinson]

In article <Jo2dnfqSRvF9IOPRnZ2dnUVZ_sidnZ2d@earthlink.com>, Michael A.
Terrell <mike.terrell@earthlink.net> writes

3/16" is between AWG 5 & AWG 4. 4 mm is between AWG 7 & AWG 6. How
much current do those kettles draw?

2kW and 3kW kettles are common. 2kW is ~8.3A, 3kW is ~12.5A. UK plugs
and sockets (=receptacles over the pond) are rated for 13A.

--
(\__/)
(='.'=)
(")_(")

 

[Mike Tomlinson]

In article <Faifo.2289$1F2.1572@newsfe21.ams2>, Arfa Daily
<arfa.daily@ntlworld.com> writes

exacerbating the thermal stresses on the
chips, their (lead-free) soldering, and the board to which they are
attached.

Which is what caused the 'red ring of death' on Microsoft's Xbox.

--
(\__/)
(='.'=)
(")_(")

 

[Michael A. Terrell]

Arfa Daily wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
news:Jo2dnfqSRvF9IOPRnZ2dnUVZ_sidnZ2d@earthlink.com...
?
? Arfa Daily wrote:
??
?? "Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
?? news:m5ednfqzQtE_8ePRnZ2dnUVZ_qWdnZ2d@earthlink.com...
?? ?
?? ? Arfa Daily wrote:
?? ??
?? ?? Well Jim, that was why I used the word "potentially", but judging by
?? the
?? ?? size of the pins used to couple the power supply's output into the
?? ?? board -
?? ?? if you've been following the thread, you will recall that I previously
?? ?? described them as being of the size you would find on the line cord
?? for a
?? ?? kettle - then I wouldn't say that there was too much in the way of
?? ?? reserve.
?? ?
?? ? "The size you would find on the line cord for a kettle" doesn't have
?? ? much meaning in the US.
??
?? Why is that ? You have electric kettles in your kitchens - I've used
?? them.
?
?
? I've never seen one. Even Coffee pots are rare these days.
?
?
?? Or don't you call them kettles ?. OK, anyway, if it's a better
?? description,
?? the size of the round ground pin on a line cord that has a three pin
?? plug.
?? Is that more meaningful ? 3/16" diameter maybe ? 4mm ?
?
?
? 3/16" is between AWG 5 ? AWG 4. 4 mm is between AWG 7 ? AWG 6. How
? much current do those kettles draw?
?
?
? --

Typical UK kettle is 2 - 3kW so 8 to 12 amps or thereabouts. Now, I'm really
confused that you say that you've never seen one. How do you boil water for
a cup of tea, or a cup of instant coffee?

On the gas or electric stove. A lot of people heat the water in a
microwave. Fast and efficient.

Whenever I come to Florida, I
stay in a private rental home, and although some have had a kettle that
heats from a ring on the cooker, I'm sure that I have also stayed in homes
that had an electric version. Or maybe I'm mistaken on this? Perhaps with
your line power at only 110v at a non 3 phase outlet, the current levels are
impractical with an element powerful enough to heat the water in short
order. Here, every home - and I really mean *every home* - has one. It is a
known problem for the electricity grid controllers, when TV ads come on in
the middle of the popular soaps. Short term demand goes through the roof, as
everyone rushes out to make a cup of tea or coffee, at the same time. The
controllers genuinely have to know the advert schedules in the TV
programmes, and factor this into their load shedding operations.

The same thing with water demand when people rush to the bathroom
during a commercial.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[Arfa Daily]

"Mike Tomlinson" <mike@jasper.org.uk> wrote in message
news:6GldFyBDtwfMFwUI@jasper.org.uk...

In article <BDDdo.2319$3p1.124@hurricane>, Arfa Daily
arfa.daily@ntlworld.com> writes

Just as a matter of interest Meat, what is your preferred brand and type
of
heatsink goop when working with these very high power processors?

I'd recommend Arctic Silver.

I have always
resisted using this stuff, because it's so messy, and so hard to remove
unless you use the complementary cleaner

nah, standard IPA works fine. The trick is to use clean tissue wetted
with IPA, wiping just once or twice then replacing with a fresh piece,
repeating until the CPU is clean. If you go back with used tissue, you
just spread the AS about more.

If it makes that much mess, you're using too much. See the application
tips on the AS website. You literally only need a half-a-grain-of-rice
sized blob in the centre of the CPU heat spreader, it'll spread out by
itself with pressure from the heatsink. Note AS say it can take a few
heat/cool cycles to become fully effective, and indeed this is what I
have found.

, but if it really is that much more
effective

It is. A colleague at work was struggling to cool a CCD (a big one!)
without having to resort to cryogenic cooling. He was experimenting
with a Peltier cooler and unable to transfer heat away from the CCD fast
enough. I suggested he try replacing the standard white goop with AS
and he was astonished at the massive improvement in heat transfer.

--
(\__/)
(='.'=)
(")_(")

Yes indeed. This is kind of what I'm finding. I in fact use a vanishingly
small amount of AS which as you say is easy to remove with IPA, but I come
across devices that have been 'excessed' on the AS by other people, and it
is very messy to remove compared to white compound. Until I really got into
using the stuff, I was of the same misconceived notion about the quantity to
use, as others seem to be. I have always been sparing with compound - and I
use a lot of it as I repair many big amps for a living - but it is a fact
that a very thin translucent layer of white, is not effective enough on a
standard non-flatted device face, and heatsink contact area, whereas with
AS, it would appear that it is. These BGAs are the size of a large graphics
chip, and I apply a very thin line of AS across the face, and then spread it
using an old credit card, rather than hoping that it will spread out across
the whole face on its own. This negates the tedious disassembly and
reassembly required to get at the heatsinking faces if the cooling turns out
to not be adequate. So far, this seems to be working well.

Arfa

 

[Jeffrey Angus]

On 9/2/2010 6:54 AM, Meat Plow wrote:

Oh and about heating water in the microwave. There is a phenomena called
hyper-boil that I'm sure you know about. Got to be careful

http://www.snopes.com/science/microwave.asp

Yeah, but your odds of having this happen are about the same
as flashing your high beams at oncoming traffic and getting
killed as a result of a gang initiation.

Jeff

 

[Meat Plow]

On Thu, 02 Sep 2010 02:59:25 -0400, Michael A. Terrell wrote:

Arfa Daily wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
news:Jo2dnfqSRvF9IOPRnZ2dnUVZ_sidnZ2d@earthlink.com... ?
? Arfa Daily wrote:
??
?? "Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
?? news:m5ednfqzQtE_8ePRnZ2dnUVZ_qWdnZ2d@earthlink.com... ?? ?
?? ? Arfa Daily wrote:
?? ??
?? ?? Well Jim, that was why I used the word "potentially", but judging
by ?? the
?? ?? size of the pins used to couple the power supply's output into
the ?? ?? board -
?? ?? if you've been following the thread, you will recall that I
previously ?? ?? described them as being of the size you would find on
the line cord ?? for a
?? ?? kettle - then I wouldn't say that there was too much in the way
of ?? ?? reserve.
?? ?
?? ? "The size you would find on the line cord for a kettle" doesn't
have ?? ? much meaning in the US.
??
?? Why is that ? You have electric kettles in your kitchens - I've used
?? them.
?
?
? I've never seen one. Even Coffee pots are rare these days. ?
?
?? Or don't you call them kettles ?. OK, anyway, if it's a better ??
description,
?? the size of the round ground pin on a line cord that has a three pin
?? plug.
?? Is that more meaningful ? 3/16" diameter maybe ? 4mm ? ?
?
? 3/16" is between AWG 5 ? AWG 4. 4 mm is between AWG 7 ? AWG 6.
How ? much current do those kettles draw? ?
?
? --

Typical UK kettle is 2 - 3kW so 8 to 12 amps or thereabouts. Now, I'm
really confused that you say that you've never seen one. How do you
boil water for a cup of tea, or a cup of instant coffee?


On the gas or electric stove. A lot of people heat the water in a
microwave. Fast and efficient.

I've evolved into the single cup K style or K-Cup Keurig machine made by
Cuisinart. Mine turns on at 5:am water is ready to brew in 2 minutes.
Place k-cup in head (could be coffee, chi-latte, hot choc, Earl Grey,)
close head and hit brew. In 45 seconds you have 12 oz of your favorite
brew. I shelved my Cuisinart Grind and Brew conventional 12 cup machine
several months ago. You can buy k-cups filled with your favorite or use
the k-cup adapter and spoon in your favorite grind.

Oh and about heating water in the microwave. There is a phenomena called
hyper-boil that I'm sure you know about. Got to be careful



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Michael A. Terrell]

Meat Plow wrote:

On Thu, 02 Sep 2010 02:59:25 -0400, Michael A. Terrell wrote:

Arfa Daily wrote:

"Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
news:Jo2dnfqSRvF9IOPRnZ2dnUVZ_sidnZ2d@earthlink.com... ?
? Arfa Daily wrote:
??
?? "Michael A. Terrell" ?mike.terrell@earthlink.net? wrote in message
?? news:m5ednfqzQtE_8ePRnZ2dnUVZ_qWdnZ2d@earthlink.com... ?? ?
?? ? Arfa Daily wrote:
?? ??
?? ?? Well Jim, that was why I used the word "potentially", but judging
by ?? the
?? ?? size of the pins used to couple the power supply's output into
the ?? ?? board -
?? ?? if you've been following the thread, you will recall that I
previously ?? ?? described them as being of the size you would find on
the line cord ?? for a
?? ?? kettle - then I wouldn't say that there was too much in the way
of ?? ?? reserve.
?? ?
?? ? "The size you would find on the line cord for a kettle" doesn't
have ?? ? much meaning in the US.
??
?? Why is that ? You have electric kettles in your kitchens - I've used
?? them.
?
?
? I've never seen one. Even Coffee pots are rare these days. ?
?
?? Or don't you call them kettles ?. OK, anyway, if it's a better ??
description,
?? the size of the round ground pin on a line cord that has a three pin
?? plug.
?? Is that more meaningful ? 3/16" diameter maybe ? 4mm ? ?
?
? 3/16" is between AWG 5 ? AWG 4. 4 mm is between AWG 7 ? AWG 6.
How ? much current do those kettles draw? ?
?
? --

Typical UK kettle is 2 - 3kW so 8 to 12 amps or thereabouts. Now, I'm
really confused that you say that you've never seen one. How do you
boil water for a cup of tea, or a cup of instant coffee?


On the gas or electric stove. A lot of people heat the water in a
microwave. Fast and efficient.

I've evolved into the single cup K style or K-Cup Keurig machine made by
Cuisinart. Mine turns on at 5:am water is ready to brew in 2 minutes.
Place k-cup in head (could be coffee, chi-latte, hot choc, Earl Grey,)
close head and hit brew. In 45 seconds you have 12 oz of your favorite
brew. I shelved my Cuisinart Grind and Brew conventional 12 cup machine
several months ago. You can buy k-cups filled with your favorite or use
the k-cup adapter and spoon in your favorite grind.

Oh and about heating water in the microwave. There is a phenomena called
hyper-boil that I'm sure you know about. Got to be careful

I let things sit for 30 seconds or more before I remove them from a
microwave.

I don't drink coffee, and I can't find the tea I like, except as a
concentrate. The price has doubled in the last year, so when i run out
of what I have, I doubt that I'll buy more.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[Meat Plow]

On Thu, 02 Sep 2010 08:03:49 -0500, Jeffrey Angus wrote:

On 9/2/2010 6:54 AM, Meat Plow wrote:
Oh and about heating water in the microwave. There is a phenomena
called hyper-boil that I'm sure you know about. Got to be careful

http://www.snopes.com/science/microwave.asp

Yeah, but your odds of having this happen are about the same as flashing
your high beams at oncoming traffic and getting killed as a result of a
gang initiation.

Some parts of the country that's a real possibility. And you wouldn't
even have to flash your lights.





--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Jeff Liebermann]

On Thu, 2 Sep 2010 02:41:15 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> wrote:

The soldering under the BGAs letting go, is the commonest problem with both
the Sony PS3 ( "yellow light of death") and the X-Box 360 ("red ring of
death")

Those names for the conditions refer to the behaviour of the front panel
indicator LEDs when the faults that result, show themselves.

I am quite convinced that the slow running of the fan at idle, is a major
contributory factor in the failing of the BGA soldering.

On the other foot, I suspect that a high air flow fan will make it
worse. The problem is NOT that the BGA is flexing with increasing
temperatures. It's that the PCB underneath the BGA is flexing.
Stabilizing the temperature of the BGA is probably useful, but unless
the PCB is also stabilized, it will bend, bulge, buckle, twist, or
otherwise go through various contortions trying deal with the
temperature difference between the BGA and the PCB. If the
differential temperature is large enough, the PCB may bulge enough to
tear way from the BGA. Again, the BGA does not move, the PCB does.

Now, add a high air flow fan into the picture and we have a larger
temperature differential. The air flow will probably do a fair job of
cooling the PCB because of the comparatively smaller mass of the PCB.
The thermal conductivity of G10/FR4 isn't all that wonderful,
resulting in a localized hot spot. With a larger difference between
the BGA area and the surrounding PCB, the result is a larger PCB bulge
with PCB air cooling. I've seen PCB's (usually motherboards) with
permanent bulges under BGA's from this effect.

For entertainment, take any PCB, heat it in the middle with a heat
gun, and watch the bulge form. It's that bulge that's ripping the
BGA's apart. Extra credit to laptop manufacturers, that add heat
sinks to the BGA, and then mechanically connects the heat sink to the
frame. When the board bends, it will literally tear the BGA off the
PCB, since the heat sink can't move with the board.

In the instructions for hot air reflowing of BGA's, there's usually a
section on pre-heating and slow cool down of the PCB. The idea is to
not tear the BGA ball apart from differential thermal expansion
between the large thermal mass of the BGA and the comparatively
smaller mass of the PCB. It's exactly like moving a solder connection
while it's cooling. You get a "cold" solder joint.

Incidentally, I once designed a 150 watt 2-30Mhz HF power amplifier.
After about a year of normal use, we started seeing failures caused by
the power transistor screws coming loose. Suspecting cold flow, I
worked on improving the grip with stainless inserts. This worked,
but now produced failures in the ceramic case power transistors. The
clue was when a PA module arrived with all the ceramic lids popped off
the transistors, but still working. Weird(tm).

After a dozen bad guesses, I determined that PCB expansion and
contraction was initially causing the loose screws. When the screws
were properly secured, the next weakest link was ripping the leads out
of the power transistor case, causing the glued lid to pop off. The
problem was solved by slightly pre-bending the power transistor leads
in a fixture so that PCB thermal expansion would be absorbed by the
bends. I still do this even on TO220 packages, which can have the
same problem. Too bad it can't be done with BGA packages.




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

 

[Jeff Liebermann]

On Thu, 02 Sep 2010 09:54:44 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

The thermal conductivity of G10/FR4 isn't all that wonderful,
(...)

Ok, let's do the numbers. The coefficient of thermal expansion for
G10/FR4 is:
1*10^-5 cm/cm/C
That means a 1 cm long piece of G10/FR4, will expand 1*10^-5 cm for
every degree C of temperature differential.

So, we have a big fat BGA chip, that's about 5cm across. It's running
hot with a bottom temperature of about 80C. Assuming the PCB is
running at room temp of 25C, that's a 55C differential temperature.
Over the diameter of the BGA, that's
125*10^-5 cm
movement of the PCB.

Solder balls come in all manner of sizes, but my guess(tm) that for a
1mm pitch BGA, a 0.4mm ball is appropriate. When soldered, the ball
will remain about the same diameter, but the height will be reduced to
about 0.1mm.

The angle that the ball moves over temperature is:
angle = arctan ( 125*10^-5 cm / 0.01cm ) = arctan 0.125
angle = 7 degrees
which is a fair amount of ball rotation. Do that often enough, and
the ball will "roll" itself off the pad. For a sanity check, solder a
rigid bar of something to a flat surface, and bend it back and forth
about 7 degrees. It will take a while, but it will eventually break.


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

 

[Arfa Daily]

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:avlv76lbbv730nj64qmotl19k485ah8ji4@4ax.com...

On Thu, 02 Sep 2010 09:54:44 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

The thermal conductivity of G10/FR4 isn't all that wonderful,
(...)

Ok, let's do the numbers. The coefficient of thermal expansion for
G10/FR4 is:
1*10^-5 cm/cm/C
That means a 1 cm long piece of G10/FR4, will expand 1*10^-5 cm for
every degree C of temperature differential.

So, we have a big fat BGA chip, that's about 5cm across. It's running
hot with a bottom temperature of about 80C. Assuming the PCB is
running at room temp of 25C, that's a 55C differential temperature.
Over the diameter of the BGA, that's
125*10^-5 cm
movement of the PCB.

Solder balls come in all manner of sizes, but my guess(tm) that for a
1mm pitch BGA, a 0.4mm ball is appropriate. When soldered, the ball
will remain about the same diameter, but the height will be reduced to
about 0.1mm.

The angle that the ball moves over temperature is:
angle = arctan ( 125*10^-5 cm / 0.01cm ) = arctan 0.125
angle = 7 degrees
which is a fair amount of ball rotation. Do that often enough, and
the ball will "roll" itself off the pad. For a sanity check, solder a
rigid bar of something to a flat surface, and bend it back and forth
about 7 degrees. It will take a while, but it will eventually break.


--
Jeff Liebermann jeffl@cruzio.com

Great info and insights in both posts as always Jeff. I will take them into
consideration. The temperature differential thing is something that I hadn't
considered, but following through your numbers, seems to be a very valid
point ...

Arfa

 

[Jeff Liebermann]

On Fri, 3 Sep 2010 02:04:18 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> wrote:

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:avlv76lbbv730nj64qmotl19k485ah8ji4@4ax.com...
On Thu, 02 Sep 2010 09:54:44 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

The thermal conductivity of G10/FR4 isn't all that wonderful,
(...)

Ok, let's do the numbers. The coefficient of thermal expansion for
G10/FR4 is:
1*10^-5 cm/cm/C
That means a 1 cm long piece of G10/FR4, will expand 1*10^-5 cm for
every degree C of temperature differential.

So, we have a big fat BGA chip, that's about 5cm across. It's running
hot with a bottom temperature of about 80C. Assuming the PCB is
running at room temp of 25C, that's a 55C differential temperature.
Over the diameter of the BGA, that's
125*10^-5 cm
movement of the PCB.

Solder balls come in all manner of sizes, but my guess(tm) that for a
1mm pitch BGA, a 0.4mm ball is appropriate. When soldered, the ball
will remain about the same diameter, but the height will be reduced to
about 0.1mm.

The angle that the ball moves over temperature is:
angle = arctan ( 125*10^-5 cm / 0.01cm ) = arctan 0.125
angle = 7 degrees
which is a fair amount of ball rotation. Do that often enough, and
the ball will "roll" itself off the pad. For a sanity check, solder a
rigid bar of something to a flat surface, and bend it back and forth
about 7 degrees. It will take a while, but it will eventually break.

Great info and insights in both posts as always Jeff. I will take them into
consideration. The temperature differential thing is something that I hadn't
considered, but following through your numbers, seems to be a very valid
point ...

Well, I did manage to make one mistake. The 7 degrees is the worst
case bending angle assuming everything accumulates in one direction.
That's not the case as local heating of the PCB will be from the
center outward. Instead of 125*10^-5 cm of lengthening measured from
the edge, the PCB will elongate half that amount, measured from the
center of the BGA. Correcting accordingly:

The angle that the ball moves over temperature is:
angle = arctan ( 63*10^-5 cm / 0.01cm ) = arctan 0.063
angle = 3.5 degrees
That's still enough to tear apart the solder ball, but not as radical
as I previously suggested.

One solution is to use a BGA adapter socket. Obviously, this isn't
going to work inside a laptop, where vertical height is a major
limitation. Same with some desktops, where the CPU heatsink and fan
can only be so tall or air flow out the top of the heatsink and fan
will be constricted. I've never tried to retrofit one of these into
an existing motherboard, but it sure looks tempting.
<http://www.advanced.com/bgastart.html>
<http://www.mill-max.com/products/newproducts_detail.cfm?pid=7>
<http://www.ironwoodelectronics.com/products/adapters/giga_snap.cfm>


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

 

[Mike Tomlinson]

In article <pXKfo.13668$45.9048@newsfe29.ams2>, Arfa Daily
<arfa.daily@ntlworld.com> writes

I have always been sparing with compound - and I
use a lot of it as I repair many big amps for a living - but it is a fact
that a very thin translucent layer of white, is not effective enough on a
standard non-flatted device face, and heatsink contact area, whereas with
AS, it would appear that it is.

Have you tried applying the white stuff to both surfaces, then scraping
it off with the edge of a card? That will fill in any valleys on both
surfaces, and you should get a good thermal bond with the minimum of
compound.

This is the method that AS suggest using, by the way.

--
(\__/)
(='.'=)
(")_(")

 

[Arfa Daily]

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:11n086hmsc5jvt998a8jr9t3nel9md1ea7@4ax.com...

On Fri, 3 Sep 2010 02:04:18 +0100, "Arfa Daily"
arfa.daily@ntlworld.com> wrote:



"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:avlv76lbbv730nj64qmotl19k485ah8ji4@4ax.com...
On Thu, 02 Sep 2010 09:54:44 -0700, Jeff Liebermann <jeffl@cruzio.com
wrote:

The thermal conductivity of G10/FR4 isn't all that wonderful,
(...)

Ok, let's do the numbers. The coefficient of thermal expansion for
G10/FR4 is:
1*10^-5 cm/cm/C
That means a 1 cm long piece of G10/FR4, will expand 1*10^-5 cm for
every degree C of temperature differential.

So, we have a big fat BGA chip, that's about 5cm across. It's running
hot with a bottom temperature of about 80C. Assuming the PCB is
running at room temp of 25C, that's a 55C differential temperature.
Over the diameter of the BGA, that's
125*10^-5 cm
movement of the PCB.

Solder balls come in all manner of sizes, but my guess(tm) that for a
1mm pitch BGA, a 0.4mm ball is appropriate. When soldered, the ball
will remain about the same diameter, but the height will be reduced to
about 0.1mm.

The angle that the ball moves over temperature is:
angle = arctan ( 125*10^-5 cm / 0.01cm ) = arctan 0.125
angle = 7 degrees
which is a fair amount of ball rotation. Do that often enough, and
the ball will "roll" itself off the pad. For a sanity check, solder a
rigid bar of something to a flat surface, and bend it back and forth
about 7 degrees. It will take a while, but it will eventually break.

Great info and insights in both posts as always Jeff. I will take them
into
consideration. The temperature differential thing is something that I
hadn't
considered, but following through your numbers, seems to be a very valid
point ...

Well, I did manage to make one mistake. The 7 degrees is the worst
case bending angle assuming everything accumulates in one direction.
That's not the case as local heating of the PCB will be from the
center outward. Instead of 125*10^-5 cm of lengthening measured from
the edge, the PCB will elongate half that amount, measured from the
center of the BGA. Correcting accordingly:

The angle that the ball moves over temperature is:
angle = arctan ( 63*10^-5 cm / 0.01cm ) = arctan 0.063
angle = 3.5 degrees
That's still enough to tear apart the solder ball, but not as radical
as I previously suggested.

One solution is to use a BGA adapter socket. Obviously, this isn't
going to work inside a laptop, where vertical height is a major
limitation. Same with some desktops, where the CPU heatsink and fan
can only be so tall or air flow out the top of the heatsink and fan
will be constricted. I've never tried to retrofit one of these into
an existing motherboard, but it sure looks tempting.
http://www.advanced.com/bgastart.html
http://www.mill-max.com/products/newproducts_detail.cfm?pid=7
http://www.ironwoodelectronics.com/products/adapters/giga_snap.cfm


--
Jeff Liebermann jeffl@cruzio.com

This is something that I was talking about with a colleague just a few days
ago. I'll take a look at the links. Going back to the differential heating
issue, I've thought a bit more about it, and it seems that the greatest
source of heat is going to be the top surface of the BGA itself, which has
the bonded heat dissipation plate for interfacing with the heatsink
assembly. Heat getting into the PCB is going to be two ways i.e. by
conduction through the solder balls, and by direct radiation from the
underside of the chip. Neither of these are going to be particularly
efficient, and I would expect as much heat as possible to be directed
upwards into the plate, by design. So it seems to me that the board is going
to remain relatively cool, compared to the underside of the BGA, and more to
the point, the upper side. So the hotter that the BGA is allowed to run, the
greater will be the undesired thermal difference between board and chip.
Therefore, any help to the cooling of the upper surface of the chip, should
help to reduce the temperature differential rather than exacerbate it,
shouldn't it ? To take it to its logical conclusion, if you could remove all
heat that the chip was generating, then there would be none to heat the
board, so there would be no thermal differential, at all ??

Arfa

 

[Arfa Daily]

"Mike Tomlinson" <mike@jasper.org.uk> wrote in message
news:R+UXbOA7ZIgMFwrh@jasper.org.uk...

In article <pXKfo.13668$45.9048@newsfe29.ams2>, Arfa Daily
arfa.daily@ntlworld.com> writes

I have always been sparing with compound - and I
use a lot of it as I repair many big amps for a living - but it is a fact
that a very thin translucent layer of white, is not effective enough on a
standard non-flatted device face, and heatsink contact area, whereas with
AS, it would appear that it is.

Have you tried applying the white stuff to both surfaces, then scraping
it off with the edge of a card? That will fill in any valleys on both
surfaces, and you should get a good thermal bond with the minimum of
compound.

This is the method that AS suggest using, by the way.

--
(\__/)
(='.'=)
(")_(")

Yes Mike. Prior to starting to use the AS, I have always treated both
surfaces when using white, contrary to much perceived wisdom where it is
insisted that only one surface should be coated. I believe in doing both
surfaces for the exact same reasons that you cite. I am also doing both
surfaces with AS, but very sparingly. There are always milling patterns on
the heatsink faces on these machines, which I think is a bit bad on the part
of the manufacturers anyway, given the huge thermal loads that are produced
by these chips ...

Arfa