Topics

Transistor solder dwell time

DW
 

I have reinstalled Q384 and Q386 transistors onto the main board of the 577 but upon soldering them back in they became fairly hot to the touch which had me concerned as I know heat is the enemy of electronics. When I removed them a fair amount of heat was involved due to the length of the leads being used on the pads, the soldering tool helped here and it appears these transistors survived the somewhat difficult removal after checking with a multimeter.

So my concern here is dwell time installing and removing transistors, especially the difficult ones which might require multiple attempts to desolder the leads and pull it out, I wonder if they make a 3 iron soldering gun in this case so all 3 leads can get heated and it can quickly be removed?

Thanks

Glenn Little
 

Eliminate the question and get proper desoldering equipment.
PACE makes very good desoldering equipment and it is available on EBay reasonable.
Hakko also makes good equipment.
These will not damage the boards nor the parts.
It will take some practice on junk boards, but it is well worth it if you repair electronics.

Glenn

On 9/17/2019 1:22 PM, DW wrote:
I have reinstalled Q384 and Q386 transistors onto the main board of the 577 but upon soldering them back in they became fairly hot to the touch which had me concerned as I know heat is the enemy of electronics. When I removed them a fair amount of heat was involved due to the length of the leads being used on the pads, the soldering tool helped here and it appears these transistors survived the somewhat difficult removal after checking with a multimeter.

So my concern here is dwell time installing and removing transistors, especially the difficult ones which might require multiple attempts to desolder the leads and pull it out, I wonder if they make a 3 iron soldering gun in this case so all 3 leads can get heated and it can quickly be removed?

Thanks


--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

Harvey White
 

There's several things to consider, one of which is that in the data sheet, there's a max temperature for the leads and time when soldering.  It's much worse with SMT parts because of the short lead length.

Is there a custom soldering tip used for desoldering?  yes, lots of them, mostly for SMT stuff that I've seen but there used to be some.  Main problem is that they were not used in a temperature controlled iron, which you really want.  You mentioned soldering gun.  Those are generally good for soldering metal parts together, but I would never use one for electronics.

You might want to look at Weller, Ungar, Hakko for ideas of what tips are available and what use they are intended for.  Most transistors are capable of withstanding temperatures on the case hot enough to burn, but with epoxy transistors, it's not going to be as obvious.

If you had a temperature controlled iron and a number of tips, you could likely make a custom desoldering tip using some sheet copper and some creative filing, and that's if you can't find anything.

Harvey

On 9/17/2019 1:22 PM, DW wrote:
I have reinstalled Q384 and Q386 transistors onto the main board of the 577 but upon soldering them back in they became fairly hot to the touch which had me concerned as I know heat is the enemy of electronics. When I removed them a fair amount of heat was involved due to the length of the leads being used on the pads, the soldering tool helped here and it appears these transistors survived the somewhat difficult removal after checking with a multimeter.

So my concern here is dwell time installing and removing transistors, especially the difficult ones which might require multiple attempts to desolder the leads and pull it out, I wonder if they make a 3 iron soldering gun in this case so all 3 leads can get heated and it can quickly be removed?

Thanks



DW
 

Thanks for the reply and very good point

I agree with you that that it does make all the difference with proper soldering equipment. I started out on a Radio Shack 10W soldering iron, it took 10 minutes to warm up but then eventually would get to hot and burn the solder, soldering with it was doable but a hassle, I had it and used it because it was conveniently laying around at the time. I have since then upgraded to a Hakko desoldering station and a Hakko desoldering gun, though not cheap they were well worth the cost and changed my experience with soldering making me more effective, especially with practice as you mentioned . I feel at least I am on the right track though it still appears that I could have done things better I am admitting to.

Dave Seiter
 

BTDT!  I have a "tip" that has a two inch wide working surface; don't recall what I used it for, but it took forever to heat up.
-Dave
---------------
 make a custom desoldering tip using some sheet copper and some 
creative filing,

Jamie Ostrowski
 

I have used those clamp-on hemostat needle-nosed type tool in the past to
act as a heat sink on the leads when I'm soldering/desoldering. Cheap and
seemed to work well. Might that be helpful?

On Tue, Sep 17, 2019 at 1:54 PM Dave Seiter <d.seiter@...> wrote:

BTDT! I have a "tip" that has a two inch wide working surface; don't
recall what I used it for, but it took forever to heat up.
-Dave
---------------
make a custom desoldering tip using some sheet copper and some
creative filing,



DW
 

"I have used those clamp-on hemostat needle-nosed type tool in the past to act as a heat sink"

I think you just gave me an idea, perhaps take a square piece of metal drill a hole in it and bolt it down with thermal compound, and when I solder the metal piece will help absorb the heat from the transistor. Maybe put it in the freezer to help even more. Well if anything I might have given someone an idea about something.

DW
 

I should mention how valuable a helpings hands tool can be, it frees up your hands and allows you to precisely position a component for soldering, and you don't burn your fingers.

Chuck Harris
 

I have taken copper flashing, cut to size, and
bent into a "U" shape to make custom desoldering
tips for the style of iron that has a screw in
tip.

I have also hammered flat a copper tip, and drilled holes
in it to fit transistor footprints. Beware when drilling
copper, it loves to grab if you use a twist drill. A home
made "D" shaped drill bit is much safer. Take a piece of
1/16 inch drill rod, grind the side flat, and sharpen to
a point. Harden it, or don't, your choice.

And, I have hammered flat a copper tip and made it spade
shaped to fit inside of transistor footprints.

I don't do that much anymore, but rather use a vacuum
desoldering station.

-Chuck Harris

DW wrote:

"I have used those clamp-on hemostat needle-nosed type tool in the past to act as a heat sink"

I think you just gave me an idea, perhaps take a square piece of metal drill a hole in it and bolt it down with thermal compound, and when I solder the metal piece will help absorb the heat from the transistor. Maybe put it in the freezer to help even more. Well if anything I might have given someone an idea about something.



Tony Fleming
 

You should show some pictures! Thanks!

On Tue, Sep 17, 2019 at 3:39 PM Chuck Harris <cfharris@...> wrote:

I have taken copper flashing, cut to size, and
bent into a "U" shape to make custom desoldering
tips for the style of iron that has a screw in
tip.

I have also hammered flat a copper tip, and drilled holes
in it to fit transistor footprints. Beware when drilling
copper, it loves to grab if you use a twist drill. A home
made "D" shaped drill bit is much safer. Take a piece of
1/16 inch drill rod, grind the side flat, and sharpen to
a point. Harden it, or don't, your choice.

And, I have hammered flat a copper tip and made it spade
shaped to fit inside of transistor footprints.

I don't do that much anymore, but rather use a vacuum
desoldering station.

-Chuck Harris

DW wrote:
"I have used those clamp-on hemostat needle-nosed type tool in the past
to act as a heat sink"

I think you just gave me an idea, perhaps take a square piece of metal
drill a hole in it and bolt it down with thermal compound, and when I
solder the metal piece will help absorb the heat from the transistor. Maybe
put it in the freezer to help even more. Well if anything I might have
given someone an idea about something.





Greg Muir
 

For leaded metal cased transistors if you are going by the case temperature as being extremely hot, you are stressing the transistor. Feeling the case is not very effective since the thermal resistance between leads and case is extremely high and by that time you have heated the silicon die to a significant temperature more hotter than the case itself. If the component lead is accessible it is wise to use a heat sink (small needle nose pliers or application specific heat sinks which can be found by Googling “soldering heat sink”) to keep from heating the device. Epoxy cased transistors are basically the same in the temperature difference between the silicon die and case temperature.

As for soldering equipment, don’t forget Metcal products. There is plenty of it used on ePay and the assortment of tips available are numerous to accommodate various applications.

As for myself I do use a Metcal iron because it utilizes RF energy to heat a small ferrite element right at the soldering tip so requiring literally no heat-up time in accordance to the heat load it encounters. In addition it somewhat regulates the heat as you work. There is no on-off action as is with many irons but, instead a continuous regulation of the heat.

I don’t use mechanized desoldering stations but, instead start part desoldering using a manual desoldering pump (such as the Edsyn “Soldapullit”) to remove the bulk of solder on the lead then follow up with a touch of solder wick if the lead is not being agreeable with removal from PWB holes. The desoldering pump adds a bit of cooling to the lead when it draws the molten solder followed by air up into its body. If the lead is still not cooperating with being removed, grabbing it with a set of small needle nose pliers while applying heat then gently wiggling it while it cools usually releases it from the connection.

Solder wick can also be helpful when being used by itself. The problem I have found is that the products with built-in rosin still don’t get the joint heated in a timely manner because they act as a heat sink by themselves. I use a small rosin pen (such as the Kester #186) to apply additional rosin to the solder wick. It gets thing going at a faster rate and certainly speeds up the time to proper joint temperature and quicker solder removal. Yes, it is an additional step to take but really helps reduce damage to the joint (as in PWB copper trace damage) and component heat-up. I also apply rosin to the leads of the device prior to installation in the circuit It also helps cut connection heating and solder application time significantly.

In all instances you should work quickly to avoid applying any more heat than necessary. And don’t use an iron with wattage higher than necessary. The nice aspect of the Metcal iron is that it only applies heat necessary to get the job done. I am not a promoter of the product but have used it for decades and have not found a better product (although an engineering colleague does swear by the Hakko products).

You might check out the Metcal site to see the tons of tips available both for regular and SMT devices. The main website is at https://www.okinternational.com/metcal. Click on the “Tips And Cartridges” button to get an idea of what they offer. Another supplier of Metcal compatible products is Thermaltronics.com. Either way, if you see something you may be interested in then go to ePay and you will probably find it at a much cheaper price most often in new condition. As for tips, if you are buying used make sure that the tips are in good condition. Of course you will also need a power unit to go with it. The tips are in categories related to a compatible power unit. There are also desoldering handpieces available as well.

Michael A. Terrell
 

I leave about one half the width of used solder wick each time that I trim
it. Put that against the lead to desolder, and apply the heat. That
transfers the heat faster, and removes to solder faster as well. If you
don't get it all out, use some 63/37 solder to fill it before making
another attempt. Wave solder was often 80/20 which his a higher melting
point but it spent less time in its plastic state. This reduced the chances
of cold solder joints caused by the component moving before it returned to
its solid state.

I used to buy 1000' surplus rolls of 1/8" braid and dip it into Kester 1544
flux between each use. 'Wet Wicking' redoces heat damage, as well. I've
pulled and reused thousands of ICs this way, along with repair over 1000 PC
boards both at a factory and in the field.

On Tue, Sep 17, 2019 at 6:25 PM Greg Muir via Groups.Io <big_sky_explorer=
yahoo.com@groups.io> wrote:

For leaded metal cased transistors if you are going by the case
temperature as being extremely hot, you are stressing the transistor.
Feeling the case is not very effective since the thermal resistance between
leads and case is extremely high and by that time you have heated the
silicon die to a significant temperature more hotter than the case itself.
If the component lead is accessible it is wise to use a heat sink (small
needle nose pliers or application specific heat sinks which can be found by
Googling “soldering heat sink”) to keep from heating the device. Epoxy
cased transistors are basically the same in the temperature difference
between the silicon die and case temperature.

As for soldering equipment, don’t forget Metcal products. There is plenty
of it used on ePay and the assortment of tips available are numerous to
accommodate various applications.

As for myself I do use a Metcal iron because it utilizes RF energy to heat
a small ferrite element right at the soldering tip so requiring literally
no heat-up time in accordance to the heat load it encounters. In addition
it somewhat regulates the heat as you work. There is no on-off action as
is with many irons but, instead a continuous regulation of the heat.

I don’t use mechanized desoldering stations but, instead start part
desoldering using a manual desoldering pump (such as the Edsyn
“Soldapullit”) to remove the bulk of solder on the lead then follow up with
a touch of solder wick if the lead is not being agreeable with removal from
PWB holes. The desoldering pump adds a bit of cooling to the lead when it
draws the molten solder followed by air up into its body. If the lead is
still not cooperating with being removed, grabbing it with a set of small
needle nose pliers while applying heat then gently wiggling it while it
cools usually releases it from the connection.

Solder wick can also be helpful when being used by itself. The problem I
have found is that the products with built-in rosin still don’t get the
joint heated in a timely manner because they act as a heat sink by
themselves. I use a small rosin pen (such as the Kester #186) to apply
additional rosin to the solder wick. It gets thing going at a faster rate
and certainly speeds up the time to proper joint temperature and quicker
solder removal. Yes, it is an additional step to take but really helps
reduce damage to the joint (as in PWB copper trace damage) and component
heat-up. I also apply rosin to the leads of the device prior to
installation in the circuit It also helps cut connection heating and
solder application time significantly.

In all instances you should work quickly to avoid applying any more heat
than necessary. And don’t use an iron with wattage higher than necessary.
The nice aspect of the Metcal iron is that it only applies heat necessary
to get the job done. I am not a promoter of the product but have used it
for decades and have not found a better product (although an engineering
colleague does swear by the Hakko products).

You might check out the Metcal site to see the tons of tips available both
for regular and SMT devices. The main website is at
https://www.okinternational.com/metcal. Click on the “Tips And
Cartridges” button to get an idea of what they offer. Another supplier of
Metcal compatible products is Thermaltronics.com. Either way, if you see
something you may be interested in then go to ePay and you will probably
find it at a much cheaper price most often in new condition. As for tips,
if you are buying used make sure that the tips are in good condition. Of
course you will also need a power unit to go with it. The tips are in
categories related to a compatible power unit. There are also desoldering
handpieces available as well.



DW
 

In the past someone on the forum mentioned chip quick to lower the melting point of solder, has anyone tried it

DW
 

Thanks for the replies, we have some ingenuity on soldering here that has sparked some do it yourself ideas I never thought of before

John Williams
 

I have found that the iron has to be quite hot in order to make the solder joint fast. The longer the iron takes to adequately fix the components together, the more heat flows Into the circuit. Tube scopes have big components that can eat up the irons heat quite quickly. To this end I plug my little iron into my Variac and turn the voltage up to 130. Make the joint fast and get out. I always wondered if everyone spits on their fingers and use them to cool the joint. Just me maybe.

Harvey White
 

Yes, and it does work as advertised, although not necessarily as you'd expect.

Firstly, you'd like to preheat the board a little, say to 100 degrees C or so, just enough to soften the paste.  Secondly, it works by mixing with the existing solder and reducing the melting point.  It will not give you the nice shiny solder joint that you expect, but it is effective.

Preheating the board in any desoldering situation is a good idea, and I've used chipquick on 144 pin flatpacks.  You'll want to go through and clean off the pins, of course.  Lots of flux can also be a good idea, and you can use it to solder sensitive parts.  Hot air gun with temperature control.  A little of this stuff goes a very long way, though.

Harvey

On 9/17/2019 7:44 PM, DW wrote:
In the past someone on the forum mentioned chip quick to lower the melting point of solder, has anyone tried it



Dave Seiter
 

I have a Craftsman soldering gun that only sees use in very special occasions (and disassembly only) when even the Weller guns aren't enough for some reason, usually due to corrosion.  The loop actually gets red/orange.  Last used on the 7503's power switch.  I normally would just cut the wires, but there was no slack to speak of.
-Dave

On Tuesday, September 17, 2019, 08:50:43 PM PDT, John Williams <books4you@...> wrote:

I have found that the iron has to be quite hot in order to make the solder joint fast. The longer the iron takes to adequately fix the components together, the more heat flows Into the circuit. Tube scopes have big components that can eat up the irons heat quite quickly. To this end I plug my little iron into my Variac and turn the voltage up to 130. Make the joint fast and get out. I always wondered if everyone spits on their fingers and use them to cool the joint. Just me maybe.

Chuck Harris
 

Excess iron heat is a commonly tried, but very wrong
way to work on big components and large ground planes.

It is like using a tack hammer to drive framing nails.
You can sometimes get away with it, but unless everything
goes perfectly, the collateral damage can be high.

With an excessively hot iron, as soon as the solder melts,
and good thermal contact happens, the joint instantly
raises to a temperature where the circuit board traces are
easily lifted.

And, the high temperature will cause the iron's solder
tinned tip to oxidize quickly, rendering it incapable of
being wetted with solder... The wet solder on the tip is
what creates the low thermal resistance necessary to get
the soldering iron's heat into the joint. So without the
wet solder on the iron's tip, even higher temperatures are
needed to overcome the high thermal resistance.

What is really needed is a tip with larger thermal mass, and
an iron with higher wattage... but with temperature control.

I am not going anywhere near your recommendation to spit
on your fingers...

-Chuck Harris

John Williams wrote:

I have found that the iron has to be quite hot in order to make the solder joint fast. The longer the iron takes to adequately fix the components together, the more heat flows Into the circuit. Tube scopes have big components that can eat up the irons heat quite quickly. To this end I plug my little iron into my Variac and turn the voltage up to 130. Make the joint fast and get out. I always wondered if everyone spits on their fingers and use them to cool the joint. Just me maybe.



Brad Thompson
 

Chuck Harris wrote on 9/17/2019 4:39 PM:

I have taken copper flashing, cut to size, and
bent into a "U" shape to make custom desoldering
tips for the style of iron that has a screw in
tip.
Hello--

IIRC, Ungar offered similar tips for their threaded-tip soldering-iron cartridges.

Various patterns were available for DIP and multilead round TO-x style packages.
If a device's leads were crimped for retention during wave soldering,
using a vacuum solder sucker and desoldering one pin at a time worked
much better.

Hardcore device salvagers who didn't care about the boards used a propane
torch and Visegrip (tm) pliers-- brutal, but surprisingly effective in
terms of recovering reusable parts. <g>

73--

Brad  AA1IP

Chuck Harris
 

Yes, crimped leads will confound most desoldering
attempts. Sometimes it is best to simply clip the
component out from the top, and tweeze the individual
lead bits, one by one. Then clear the holes for the
new part.

In China, the uhmm???... let me call them scrapyard
peasants... hang around fire barrels burning trash and
old pallets, heating the boards over the trash fires.
When the solder melts, they flip the board over, and
smack it against the rim of another barrel. Large
boards have to go through several cycles of heating
and rapping.

The stuck together solder and electric part contents
of that barrel are sold to still other peasants for
processing. They put chunks of solder crusted parts
into steel fryer baskets, and cook them in fryer vats
full of boiling peanut oil. They then shake off any
loose solder blobs and oil, and dip the parts in any
old solvent (gasoline, diesel, perc...) to wash off
the peanut oil residue.

Presumably, when the restaurant re-opens, the fryers
resume their usual task of making egg rolls and
fried wanton...

The "cleaned parts" then move on to sorters and lead
welders that strip them of gold, weld on extension
leads, tin them, add new date codes, and part numbers,
and sell them as new on ebay.

-Chuck Harris

Brad Thompson wrote:
Chuck Harris wrote on 9/17/2019 4:39 PM:
...
Hardcore device salvagers who didn't care about the boards used a propane
torch and Visegrip (tm) pliers-- brutal, but surprisingly effective in
terms of recovering reusable parts. <g>

73--

Brad AA1IP