I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

SAUHING LEE wrote:

I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

When I was developing my homebrew hotair station
( http://www.cybertheque.org/homebrew/smt-rework-tool ) I found that
a few simple tests helped while setting temperature and airflow. These
tests are not intended to be quantitative, merely to indicate basic
functionality.

1. Basic temp test is to direct the airflow at a piece of bond writing or
typing paper at a distance of about one-half inch (13mm); it should
blacken a spot in one second at your chosen air velocity.

2. Use a scrap board with SMT components to experiment with air
velocity and temperature settings; airflow that doesn't blow away the
smallest components when used with the minimum temperature that reflows
the solder within a couple of seconds is ideal. Increase temperature
and airflow for larger components as determined by experiment. Note
the settings for production use.

It can't hurt to calibrate you settings with proper temperature probes
and pressure gauges. My station has an accurate low-velocity air gauge
but as of yet no temp. probes.

Michael

SAUHING LEE wrote in news:49e06cf0-a934-4b23-b83f-
:

I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

There is no reason to go about 225 C (437 F), for any normal solder, and,
if you remember the book title by Robert Henlein, paper doesn't burn till
you get to 451.

[quote]
C F
183 361.4 63/37 It has the lowest melting point (183 °C or 361.4 °F)
of all the tin/lead alloys; and
220 428 SnAg3.0Cu0.5, tin with 3% silver and 0.5% copper, has a
melting point of 217 to 220 °C
218 424.4 SnAg3.5Cu0.7 is another commonly used alloy, with melting
point of 217-218 °C.
217 422.6 SnAg3.5Cu0.9, with melting point of 217 °C, is determined
by NIST to be truly eutectic.
218 424.4 SnAg3.8Cu0.7, with melting point 217-218 °C, is preferred
by the European IDEALS consortium for reflow soldering.
223 433.4 SnAg3.8Cu0.7Sb0.25 is preferred by the European IDEALS
consortium for wave soldering.
32 SnAg3.9Cu0.6, with melting point 217-223 °C, is recommended by
the US NEMI consortium for reflow soldering.
32
227 440.6 SnCu0.7, with melting point of 227 °C, is a cheap
alternative for wave soldering, recommended by the US NEMI consortium.
199 390.2 SnZn9, with melting point of 199 °C, is a cheaper alloy but
is prone to corrosion and oxidation.
198 388.4 SnZn8Bi3, with melting point of 191-198 °C, is also prone
to corrosion and oxidation due to its zinc content.
240 464 SnSb5, tin with 5% of antimony, is the US plumbing industry
standard. Its melting point is 232-240 °C. It displays good resistance to
thermal fatigue and good shear strength.
225 437 SnAg2.5Cu0.8Sb0.5 melts at 217-225 °C and is patented by AIM
alliance.
208 406.4 SnIn8.0Ag3.5Bi0.5 melts at 197 to 208 °C and is patented by
Matsu****a/Panasonic.
139 282.2 SnBi57Ag1 melts at 137-139 °C and is patented by Motorola.
138 280.4 SnBi58 melts at 138 °C.
118 244.4 SnIn52 melts at 118 °C and is suitable for the cases where
low-temperature soldering is needed.
[unquote]

It looks like your 420 may be a bit too low. 433.4, 437 or 440.6 might be
necessary.





--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

SAUHING LEE wrote in message
...
I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

Can you beg or borrow a thermocouple to independently confirm the settings ?
Airflow rates you can check with element off or very low and part filling a
rubbish sack in a certain time.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

In article 39,
bz wrote:

There is no reason to go about 225 C (437 F), for any normal solder, and,
if you remember the book title by Robert Henlein, paper doesn't burn till
you get to 451.

I disagree. In order to get the solder to acquire melting temperature in
any reasonable length of time, the heat source has to be far above the
temps you mention. It is tedious to hand solder with a tip that is less
than 800 F, and desoldering requires similar temps. The problem lies in
heat transfer and loss.

Smitty Two wrote in
news
In article 39,
bz wrote:

There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Henlein, paper doesn't
burn till you get to 451.

I disagree. In order to get the solder to acquire melting temperature in
any reasonable length of time, the heat source has to be far above the
temps you mention. It is tedious to hand solder with a tip that is less
than 800 F, and desoldering requires similar temps. The problem lies in
heat transfer and loss.

You mistake the transfer of heat (calories) for temperature.
This is a common mistake.

The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of the
soldering iron and the power of the heating element.

For soldering irons, there are two philosophies.
1) use a hot enough iron to rapidly transfer heat to the target and remove
the iron before the temperature gets high enough to damage the parts.
Often the iron does NOT have enough power to raise a large object to
the iron temperature. This can make for both over heated components and
cold soldered joints.

2) use a temperature controlled iron that has enough heat capacity and
conductivity to rapidly heat the target to the soldering temperature.
In the second case, it is NOT important to remove the iron quickly
because it will NOT overheat the components.

Given good heat conductivity (clean and tight joints in the iron) and
sufficient heat capacity (plenty of watts), a temperature controlled iron
is much better. The iron temperature should be set slightly higher than
the melting temperature of the solder. There is no need for dozens or
hundreds of degrees in excess of the melting temperature.

In the case of a hot air gun, when there is sufficient heating capacity
and air flow, everything within the area of the air flow will be quickly
brought to the set temperature.

caveat: Many components are rated for limited exposure to higher
temperatures. I don't know of ANY transistors or ICs that are rated to
withstand 800 F degrees for any length of time.

Final point: using the correct solder is important also. True eutectic
solders are best because they melt and 'freeze' at a single temperature.

Non eutectic alloys, like 50/50 or 60/40, pass through a 'plastic stage'
where crystals of one of the components start to form.

Any movement while the joint cools through the 'plastic stage' temperature
range results in a 'cold solder joint' where there are actually separate
crystals of the component metals and conductivity is unreliable.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Henlein, paper doesn't
burn till you get to 451.

I disagree. In order to get the solder to acquire melting temperature in
any reasonable length of time, the heat source has to be far above the
temps you mention. It is tedious to hand solder with a tip that is less
than 800 F, and desoldering requires similar temps. The problem lies in
heat transfer and loss.

You mistake the transfer of heat (calories) for temperature.
This is a common mistake.

I don't believe I'm mistaking the two, but I'm willing to be corrected
if you'll point out my error more clearly.

The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of the
soldering iron and the power of the heating element.

For soldering irons, there are two philosophies.
1) use a hot enough iron to rapidly transfer heat to the target and remove
the iron before the temperature gets high enough to damage the parts.
Often the iron does NOT have enough power to raise a large object to
the iron temperature. This can make for both over heated components and
cold soldered joints.

2) use a temperature controlled iron that has enough heat capacity and
conductivity to rapidly heat the target to the soldering temperature.
In the second case, it is NOT important to remove the iron quickly
because it will NOT overheat the components.

I keep thinking that you speak from theory, not practice. It is
virtually impossible to solder with a 500 F iron, yet many components
supposedly can't stand even that for more than 5 seconds.


Given good heat conductivity (clean and tight joints in the iron) and
sufficient heat capacity (plenty of watts), a temperature controlled iron
is much better. The iron temperature should be set slightly higher than
the melting temperature of the solder. There is no need for dozens or
hundreds of degrees in excess of the melting temperature.

We disagree quite strongly on this point, and I wonder on what you base
your perspective? Many, many years ago, the military presumed to insist
on 600F, and that proved to be woefully inadequate for hand soldering.
Now, a solder bath, having an immense thermal mass, as well as providing
virtually total joint immersion, can solder well at 500. But hand
soldering with any measure of expediency requires *at least* 700, and in
my experience, 800 is far better.


In the case of a hot air gun, when there is sufficient heating capacity
and air flow, everything within the area of the air flow will be quickly
brought to the set temperature.

Hot air guns are much, much hotter than the melting point of solder. Why
would that be, if the very low temps you advocate are actually
sufficient?

caveat: Many components are rated for limited exposure to higher
temperatures. I don't know of ANY transistors or ICs that are rated to
withstand 800 F degrees for any length of time.

True. And they needn't be exposed very long. Through-hole ICs and
transistors may need approx. 1 second per lead. With a typical 16 pin
surface mount IC, three seconds is plenty to skate down one side and
solder all 8 pins, at 800F.


Final point: using the correct solder is important also. True eutectic
solders are best because they melt and 'freeze' at a single temperature.

Non eutectic alloys, like 50/50 or 60/40, pass through a 'plastic stage'
where crystals of one of the components start to form.

And we had a discussion here not long ago, begun with the question of
why anyone would use anything other than 63/37, assuming a leaded
formulation. As I recall, no one offered any very plausible reason to
use anything else.


Any movement while the joint cools through the 'plastic stage' temperature
range results in a 'cold solder joint' where there are actually separate
crystals of the component metals and conductivity is unreliable.

"bz" wrote in message
98.139...
SAUHING LEE wrote in news:49e06cf0-a934-4b23-b83f-
:

I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater and
the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)

This is the first hot air station that i has, so i don't know whether
the machines is defective or something is wrong?

Any suggestion?

There is no reason to go about 225 C (437 F), for any normal solder, and,
if you remember the book title by Robert Henlein, paper doesn't burn till
you get to 451.

And Fahrenheit 451 was written by Ray Bradbury,
not Robert Heinlein.

Deke

"Deke" no wrote in
:


"bz" wrote in message
98.139...
SAUHING LEE wrote in
news:49e06cf0-a934-4b23-b83f-
:

I 've just bought a used hakko 852 hot air smd rework station.

After i press the start button, the heater heat up and the air start
blowing(orange color from the heater). When the sensor detects the
desired temperature, there will be no orange color from the heater
and the air is still blowing.

I tried many times to remove a small diode with temperature at 420,
but the hot air is not hot enough. And the diode still stick to the
board(i test it with a tweezer)
.....
There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Henlein, paper doesn't
burn till you get to 451.

And Fahrenheit 451 was written by Ray Bradbury,
not Robert Heinlein.

You are correct. I was wrong on the author. Both wrote good stories but I
misattributed. My bad. Sorry.


Deke







--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

Smitty Two wrote in
news
In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Heinlein, paper
doesn't burn till you get to 451.
[correction, Ray Bradbury, not RH. Sorry!]

I disagree. In order to get the solder to acquire melting temperature
in any reasonable length of time, the heat source has to be far above
the temps you mention. It is tedious to hand solder with a tip that
is less than 800 F, and desoldering requires similar temps. The
problem lies in heat transfer and loss.

You mistake the transfer of heat (calories) for temperature.
This is a common mistake.

I don't believe I'm mistaking the two, but I'm willing to be corrected
if you'll point out my error more clearly.

If the explanation that I gave was not clear, enough, I suggest the study
of thermodynamics and heat transfer. http://en.wikipedia.org/wiki/Heat is
a good place to start.

The raising of the temperature to the melting point of the solder requires
the transfer of a sufficient number of calories to the component. This does
NOT require a high temperature, it just requires efficient heat transfer.


The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of the
soldering iron and the power of the heating element.

For soldering irons, there are two philosophies.
1) use a hot enough iron to rapidly transfer heat to the target and
remove the iron before the temperature gets high enough to damage the
parts.
Often the iron does NOT have enough power to raise a large object to
the iron temperature. This can make for both over heated components
and cold soldered joints.

2) use a temperature controlled iron that has enough heat capacity and
conductivity to rapidly heat the target to the soldering temperature.
In the second case, it is NOT important to remove the iron quickly
because it will NOT overheat the components.

I keep thinking that you speak from theory, not practice.

Incorrect. I soldered my first connections in the late 50's. When I was 8
years old.

First connections were made with 50/50 solder. Well I remember trying to
hold the lead perfectly stationary while my fingers burned.

I was first licensed as a ham in 1961 as WN5DQP at age 16.
I built Heathkit TVs and Scopes in the early 60's. Using 60/40 solder.

I worked on a resistor/capacitor production line in the late 60's, early
70's.

First as a Process Technician then as a Process Engineer for Sprague
Electric Co. I WROTE process specifications for Sprague's production line
for soldering capacitors to their leads in the early 70's.

After the 'mini recession' in the early 70's I went into consumer
electronic service. I owned a consumer electronics repair shop in the
70's. Got a bit of practical experience there.

In 74-76, I fixed radars and electronics on ships on the Mississippi. Got
a bit of practical experience there also.

I did board repair on DEC and DG computers in the late 70's. Component
level repairs on PCBs.

A couple of years ago, I built an Elecraft K2/100 ham transceiver.

Recently, I built several SoftRock RXTX SDR radios, using SMT components.

I think that qualifies as a bit of practice to go with a bit of theoretical
knowledge, a BS in Chemistry, 1970.

It is
virtually impossible to solder with a 500 F iron,

I don't find that to be true. All one needs is a good clean iron properly
tinned, good 63/37 solder, and a good flux pen, clean, pretinned leads on
the components, a clean, pretinned PCB and proper technique.

Of course, ANY oxide (and solder does oxidize rapidly) on the tip of the iron
and you have just added thermal resistance. The iron tip MUST be freshly
cleaned and tinned.

yet many components
supposedly can't stand even that for more than 5 seconds.

Many components CAN'T.


Given good heat conductivity (clean and tight joints in the iron) and
sufficient heat capacity (plenty of watts), a temperature controlled
iron is much better. The iron temperature should be set slightly higher
than the melting temperature of the solder. There is no need for dozens
or hundreds of degrees in excess of the melting temperature.

We disagree quite strongly on this point

As I said originally, there are two philosophies.

, and I wonder on what you base
your perspective? Many, many years ago, the military presumed to insist
on 600F, and that proved to be woefully inadequate for hand soldering.

This is true, IF the iron is not clean or is underpowered. The point at
which a temperature controlled iron measures the temperature is also
important. The nearer the tip, the better.

Now, a solder bath, having an immense thermal mass, as well as providing
virtually total joint immersion, can solder well at 500.

Correct.

If I recall correctly, our 95/5 (tin/silver) solder pots ran at
495F(257C). The 62/36/2 pots ran considerably cooler but I don't remember
the numbers. There was a layer of hot wax on top of the solder to 'preheat'
the parts and protect the solder from oxidizing.

But hand
soldering with any measure of expediency requires *at least* 700, and in
my experience, 800 is far better.

Once you get the joint above the melting point of the solder, there is no
need for higher temperature. Proper heat transfer is the key.


In the case of a hot air gun, when there is sufficient heating capacity
and air flow, everything within the area of the air flow will be
quickly brought to the set temperature.

Hot air guns are much, much hotter than the melting point of solder.

Depends on the settings of the gun. My 'CSI Hot air gun 2'
http://www.web-tronics.com/hotairgunwdi.html
solders and desolders quite well at temperatures not much greater than the
melting point of the solder.

I have soldered and removed 48 lead SMT ICs without damaging the
surrounding SMT components. I have removed and later reused 8 lead SMT
ICs. This was done without badly charing the paper dams around the parts.
The paper WAS heated to a light brown so I believe the digital read out on
the hot-air gun.

Why
would that be, if the very low temps you advocate are actually
sufficient?

My hot air gun WILL go hotter, but after playing around with it for some
time, salvaging parts from old PCBs, I found that I could work quite well
with much lower temperatures than I had first tried. Nozzel size and air flow
rate are very important. The nozzel must be large enough to heat the area and
the flow rate must be sufficient to do so quickly.


caveat: Many components are rated for limited exposure to higher
temperatures. I don't know of ANY transistors or ICs that are rated to
withstand 800 F degrees for any length of time.

True. And they needn't be exposed very long. Through-hole ICs and
transistors may need approx. 1 second per lead. With a typical 16 pin
surface mount IC, three seconds is plenty to skate down one side and
solder all 8 pins, at 800F.

Or even at 440 F, with 63/37 solder, and then to 'mop up' with clean, well
fluxed solder braid.

One 48 lead component I worked with recently has an absolute max of
300C(572F) for 10 seconds.

Your 800F is 427C. There is a very good chance of damaging such an IC at
that temperature.


Final point: using the correct solder is important also. True eutectic
solders are best because they melt and 'freeze' at a single
temperature.

Non eutectic alloys, like 50/50 or 60/40, pass through a 'plastic
stage' where crystals of one of the components start to form.

And we had a discussion here not long ago, begun with the question of
why anyone would use anything other than 63/37, assuming a leaded
formulation. As I recall, no one offered any very plausible reason to
use anything else.

A small percentage of silver helps prevent leaching of silver from some
components and is vital for the mounting strips in some Tektronix scopes.
A small percentage of copper helps prevent leaching of copper from PCB
traces.

Any movement while the joint cools through the 'plastic stage'
temperature range results in a 'cold solder joint' where there are
actually separate crystals of the component metals and conductivity is
unreliable.



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

There is no reason to go about 225 C (437 F), for any normal solder,
and, if you remember the book title by Robert Heinlein, paper
doesn't burn till you get to 451.
[correction, Ray Bradbury, not RH. Sorry!]

I disagree. In order to get the solder to acquire melting temperature
in any reasonable length of time, the heat source has to be far above
the temps you mention. It is tedious to hand solder with a tip that
is less than 800 F, and desoldering requires similar temps. The
problem lies in heat transfer and loss.

You mistake the transfer of heat (calories) for temperature.
This is a common mistake.

I don't believe I'm mistaking the two, but I'm willing to be corrected
if you'll point out my error more clearly.

If the explanation that I gave was not clear, enough, I suggest the study
of thermodynamics and heat transfer. http://en.wikipedia.org/wiki/Heat is
a good place to start.

It isn't your explanation that lacks, only your suggestion that I'm
confused on the topic.


The raising of the temperature to the melting point of the solder requires
the transfer of a sufficient number of calories to the component. This does
NOT require a high temperature, it just requires efficient heat transfer.

I agree. Unfortunately, efficient heat transfer is difficult to
impossible in many hand soldering applications. The excess temperature
to a small contact area makes up for that.



The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of the
soldering iron and the power of the heating element.

Contact area is the holy grail of efficient heat transfer.


For soldering irons, there are two philosophies.
1) use a hot enough iron to rapidly transfer heat to the target and
remove the iron before the temperature gets high enough to damage the
parts.
Often the iron does NOT have enough power to raise a large object to
the iron temperature. This can make for both over heated components
and cold soldered joints.

2) use a temperature controlled iron that has enough heat capacity and
conductivity to rapidly heat the target to the soldering temperature.
In the second case, it is NOT important to remove the iron quickly
because it will NOT overheat the components.

I keep thinking that you speak from theory, not practice.

Incorrect. I soldered my first connections in the late 50's. When I was 8
years old.

First connections were made with 50/50 solder. Well I remember trying to
hold the lead perfectly stationary while my fingers burned.

I was first licensed as a ham in 1961 as WN5DQP at age 16.
I built Heathkit TVs and Scopes in the early 60's. Using 60/40 solder.

I worked on a resistor/capacitor production line in the late 60's, early
70's.

First as a Process Technician then as a Process Engineer for Sprague
Electric Co. I WROTE process specifications for Sprague's production line
for soldering capacitors to their leads in the early 70's.

After the 'mini recession' in the early 70's I went into consumer
electronic service. I owned a consumer electronics repair shop in the
70's. Got a bit of practical experience there.

In 74-76, I fixed radars and electronics on ships on the Mississippi. Got
a bit of practical experience there also.

I did board repair on DEC and DG computers in the late 70's. Component
level repairs on PCBs.

A couple of years ago, I built an Elecraft K2/100 ham transceiver.

Recently, I built several SoftRock RXTX SDR radios, using SMT components.

I think that qualifies as a bit of practice to go with a bit of theoretical
knowledge, a BS in Chemistry, 1970.

Credentials accepted.


It is
virtually impossible to solder with a 500 F iron,

I don't find that to be true. All one needs is a good clean iron properly
tinned, good 63/37 solder, and a good flux pen, clean, pretinned leads on
the components, a clean, pretinned PCB and proper technique.

How long does it take you to make one solder connection on a 1/4 watt
through-hole resistor on a typical board two-sided board with plated
through holes, at 500F? I ask because in production, 3 seconds is far
beyond unacceptable.


Of course, ANY oxide (and solder does oxidize rapidly) on the tip of the iron

and you have just added thermal resistance. The iron tip MUST be freshly
cleaned and tinned.

yet many components
supposedly can't stand even that for more than 5 seconds.

Many components CAN'T.

Then why do you assert that with low temps, component damage is
impossible?



Given good heat conductivity (clean and tight joints in the iron) and
sufficient heat capacity (plenty of watts), a temperature controlled
iron is much better. The iron temperature should be set slightly higher
than the melting temperature of the solder. There is no need for dozens
or hundreds of degrees in excess of the melting temperature.

We disagree quite strongly on this point

As I said originally, there are two philosophies.

And one of them works in practice!


, and I wonder on what you base
your perspective? Many, many years ago, the military presumed to insist
on 600F, and that proved to be woefully inadequate for hand soldering.

This is true, IF the iron is not clean or is underpowered. The point at
which a temperature controlled iron measures the temperature is also
important. The nearer the tip, the better.

Now, a solder bath, having an immense thermal mass, as well as providing
virtually total joint immersion, can solder well at 500.

Correct.

If I recall correctly, our 95/5 (tin/silver) solder pots ran at
495F(257C). The 62/36/2 pots ran considerably cooler but I don't remember
the numbers. There was a layer of hot wax on top of the solder to 'preheat'
the parts and protect the solder from oxidizing.

But hand
soldering with any measure of expediency requires *at least* 700, and in
my experience, 800 is far better.

Once you get the joint above the melting point of the solder, there is no
need for higher temperature. Proper heat transfer is the key.

See above.



In the case of a hot air gun, when there is sufficient heating capacity
and air flow, everything within the area of the air flow will be
quickly brought to the set temperature.

Hot air guns are much, much hotter than the melting point of solder.

Depends on the settings of the gun. My 'CSI Hot air gun 2'
http://www.web-tronics.com/hotairgunwdi.html
solders and desolders quite well at temperatures not much greater than the
melting point of the solder.

I have soldered and removed 48 lead SMT ICs without damaging the
surrounding SMT components. I have removed and later reused 8 lead SMT
ICs. This was done without badly charing the paper dams around the parts.
The paper WAS heated to a light brown so I believe the digital read out on
the hot-air gun.

Why
would that be, if the very low temps you advocate are actually
sufficient?

My hot air gun WILL go hotter, but after playing around with it for some
time, salvaging parts from old PCBs, I found that I could work quite well
with much lower temperatures than I had first tried. Nozzel size and air flow
rate are very important. The nozzel must be large enough to heat the area and
the flow rate must be sufficient to do so quickly.


caveat: Many components are rated for limited exposure to higher
temperatures. I don't know of ANY transistors or ICs that are rated to
withstand 800 F degrees for any length of time.

True. And they needn't be exposed very long. Through-hole ICs and
transistors may need approx. 1 second per lead. With a typical 16 pin
surface mount IC, three seconds is plenty to skate down one side and
solder all 8 pins, at 800F.

Or even at 440 F, with 63/37 solder, and then to 'mop up' with clean, well
fluxed solder braid.

One 48 lead component I worked with recently has an absolute max of
300C(572F) for 10 seconds.

Your 800F is 427C. There is a very good chance of damaging such an IC at
that temperature.

We do it all day long every day. Less than 1/2 second per lead. No
damage.



Final point: using the correct solder is important also. True eutectic
solders are best because they melt and 'freeze' at a single
temperature.

Non eutectic alloys, like 50/50 or 60/40, pass through a 'plastic
stage' where crystals of one of the components start to form.

And we had a discussion here not long ago, begun with the question of
why anyone would use anything other than 63/37, assuming a leaded
formulation. As I recall, no one offered any very plausible reason to
use anything else.

A small percentage of silver helps prevent leaching of silver from some
components and is vital for the mounting strips in some Tektronix scopes.
A small percentage of copper helps prevent leaching of copper from PCB
traces.

I'll accept your assertions. The original dialogue to which I refer
concerned only tin/lead mixtures.


Any movement while the joint cools through the 'plastic stage'
temperature range results in a 'cold solder joint' where there are
actually separate crystals of the component metals and conductivity is
unreliable.

Smitty Two wrote in
news
In article 39,
bz wrote:

Smitty Two wrote in
news
In article 39,
bz wrote:

.....
If the explanation that I gave was not clear, enough, I suggest the
study of thermodynamics and heat transfer.
http://en.wikipedia.org/wiki/Heat is a good place to start.

It isn't your explanation that lacks, only your suggestion that I'm
confused on the topic.

Sorry. I didn't intend to imply that I could read your mind, just that many
people confuse temperature and heat. Many of those that confuse the two
think that a higher temperature is better for soldering.


The raising of the temperature to the melting point of the solder
requires the transfer of a sufficient number of calories to the
component. This does NOT require a high temperature, it just requires
efficient heat transfer.

I agree. Unfortunately, efficient heat transfer is difficult to
impossible in many hand soldering applications. The excess temperature
to a small contact area makes up for that.

A clean iron, well tinned, clean circuit board and component lead, fluxed.
Clean the iron just before you bring it to the joint to be soldered.
Clean it by plunging it into a tangle of stainless steel shavings (a pot
scouring pad) and twisting as you remove it. The shavings do NOT cool the
iron like a sponge would.

Use thin solder. Put the solder against the component lead and board.
Touch the iron to the solder, board and component lead, all at the same
time.

Feed enough solder to wet the surfaces and encourage good heat transfer.
For leaded components, move the solder wire around to the other side of the
joint and make sure all wets well and you get a good solder fillet.

1/2 second should be enough.

The rate of heat transfer depends on TWO things: the difference in
temperature and the heat conductivity. In soldering there are other
important factors that often comes into play, the heat capacity of
the soldering iron and the power of the heating element.

Contact area is the holy grail of efficient heat transfer.

EXACTLY CORRECT! [for conductive heat transfer].
CLEAN contact area is vital.
.....

It is
virtually impossible to solder with a 500 F iron,

I don't find that to be true. All one needs is a good clean iron
properly tinned, good 63/37 solder, and a good flux pen, clean,
pretinned leads on the components, a clean, pretinned PCB and proper
technique.

How long does it take you to make one solder connection on a 1/4 watt
through-hole resistor on a typical board two-sided board with plated
through holes, at 500F? I ask because in production, 3 seconds is far
beyond unacceptable.


In production, the board is preheated before it reaches the solder fountain
and spends a couple of seconds in the fountain. It is then cooled at a
controlled rate to avoid temperature shock.

Or the solder paste is silk screen printed onto the board, the parts are
robot applied.
The board is then preheated for several minutes, the temperature is quickly
ramped up to the melting point of the solder and back down.
The board is then cooled and cleaned. This is done as the board is carried
by a belt through the different temperature zones.

Of course, ANY oxide (and solder does oxidize rapidly) on the tip of
the iron

and you have just added thermal resistance. The iron tip MUST be
freshly cleaned and tinned.

yet many components
supposedly can't stand even that for more than 5 seconds.

Many components CAN'T.

Then why do you assert that with low temps, component damage is
impossible?

I certainly didn't mean that component damage is impossible.

Let me restate my opinion:
It is easier to solder without damaging components using a clean, high
wattage, controlled temperature iron set at a temperature slightly above
the melting point of the solder
than it is when using a low wattage, high temperature iron.

With practice, either method can be used, but I have tried both and prefer
high wattage, with a lower, controlled temperature.

Given good heat conductivity (clean and tight joints in the iron)
and sufficient heat capacity (plenty of watts), a temperature
controlled iron is much better. The iron temperature should be set
slightly higher than the melting temperature of the solder. There is
no need for dozens or hundreds of degrees in excess of the melting
temperature.

We disagree quite strongly on this point

As I said originally, there are two philosophies.

And one of them works in practice!

BOTH work, in practice.

With proper [different] techniques, both can be used.

.....

Once you get the joint above the melting point of the solder, there is
no need for higher temperature. Proper heat transfer is the key.

See above.


.....
Your 800F is 427C. There is a very good chance of damaging such an IC
at that temperature.

We do it all day long every day. Less than 1/2 second per lead. No
damage.

Yep. And I have seen what happens when the iron stays on the joint 1/2
second too long.
I have had to change ICs that failed because of overheating.

I have also had to work with non temperature controlled irons, even battery
powered ones.

I would ALWAYS prefer to have a high wattage (150W) temperature controlled
iron set to 500 or so degrees rather than a 15 W 900 degree iron.
You are, of course, welcome to use what you prefer.
As I said, BOTH methods can be made to work.

Best regards. I suspect that we have exhausted the subject for now.



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

Smitty Two wrote:

In order to get the solder to acquire melting temperature in
any reasonable length of time, the heat source has to be far above the
temps you mention.

The discussion seems to avoid the point, that the parts
to be desoldered sit on a base of polymerized organics.

I got the impression, that even at moderate temperatures,
which allow a relative quick separation of parts from the
boards, a notable depolymerization takes place, with the
effect, that the monomers lounge in your clothing for several
days, as far as you did not inhale them.

Regards,
H.