Hi, all. Need some tips on soldering and unsoldering MOSFETs.

On unsoldering (bad) ones: They are of the types with fins soldered on to
the surface of the board. Do I just apply heat to the top of the fin (D),
and then lift the MOSFET to an upright position before unsoldering its two
outer legs (G & S)?

On soldering good ones: Are there any heat precaution when soldering a new
MOSFET? Should I clamp the top of MOSFET to a heat sink before applying heat
to its legs? Would a 40W iron be too hot for the job for an amateur hand?

Thanks
Al-U

"alpha_uma" wrote in message
news:UChQc.13636$gE.8616@pd7tw3no...
Hi, all. Need some tips on soldering and unsoldering MOSFETs.

On unsoldering (bad) ones: They are of the types with fins soldered on to
the surface of the board. Do I just apply heat to the top of the fin (D),
and then lift the MOSFET to an upright position before unsoldering its two
outer legs (G & S)?

If you have no intention of reusing them, cut the leads first (close to the
device). Grab the device with pliers and apply heat. Then, remove the
leads one at a time.

On soldering good ones: Are there any heat precaution when soldering a new
MOSFET? Should I clamp the top of MOSFET to a heat sink before applying
heat
to its legs? Would a 40W iron be too hot for the job for an amateur hand?

40 W is about right for the device itself and is OK for the leads if you
work quickly. However, you might get delamination of the foil on some
circuit boards.

alpha_uma wrote:

Hi, all. Need some tips on soldering and unsoldering MOSFETs.

On unsoldering (bad) ones: They are of the types with fins soldered on to
the surface of the board. Do I just apply heat to the top of the fin (D),
and then lift the MOSFET to an upright position before unsoldering its two
outer legs (G & S)?

On soldering good ones: Are there any heat precaution when soldering a new
MOSFET? Should I clamp the top of MOSFET to a heat sink before applying heat
to its legs? Would a 40W iron be too hot for the job for an amateur hand?

Thanks
Al-U

Quoting from a private discussion with someone who replaces lots of
MOSFETs (I assume he won't mind):

There's one other thing I forgot to tell you.
The power fets can be removed/replaced using a very wide tip. First lift the
outer legs, then idea is to spread the heat evenly across the entire tab/pad
area. wet the pad & tab with some kester "44" solder, then apply the wide tip
in a manner that gives the most surface area contact, at the same time grasp
one of the legs with needle nose pliers, the fet will come right off.
I keep some alcohol in a small dish to drop the fet in so it doesn't stay hot &
possibly damage it (if I am not sure it's good).
To install a new fet, use the same wide tip & wick the pad very clean, then
wet the pad with a very thin coat of silver based solder, let the pad cool,
align the new fet & tack the legs to hold it as aligned as possible, now heat
the pad & re-wet while using a wooden dowel to apply slight pressure to the new
fet, as soon as you see complete flow & the fet sinks into position, remove the
heat, hold the fet for a few seconds then use an alcohol soaked q-tip to cool
the fet.
I replaced a lot of these fets before I was able to make it look good.

Sunny

Easiest way to remove surface mount components is a temparature controlled
heat gun. It takes some practice so you don't burn up PCB's or lift traces,
but when you get comfortable with it it only takes 30 sec to remove a part.
I have met a servicer in Nashville who only uses a Weller Pyropen to do all
his surface mount stuff. He's done a lot of Pioneer plasmas, so I guess he's
really good at it. 600deg F is usually OK for most things.


--
Jammy Harbin
J & J Electronics, Inc.
227 S. 4th St.
Selmer, TN 38375
731-645-3311
"Sunny" wrote in message
...


alpha_uma wrote:

Hi, all. Need some tips on soldering and unsoldering MOSFETs.

On unsoldering (bad) ones: They are of the types with fins soldered on
to
the surface of the board. Do I just apply heat to the top of the fin
(D),
and then lift the MOSFET to an upright position before unsoldering its
two
outer legs (G & S)?

On soldering good ones: Are there any heat precaution when soldering a
new
MOSFET? Should I clamp the top of MOSFET to a heat sink before applying
heat
to its legs? Would a 40W iron be too hot for the job for an amateur
hand?

Thanks
Al-U

Quoting from a private discussion with someone who replaces lots of
MOSFETs (I assume he won't mind):

There's one other thing I forgot to tell you.
The power fets can be removed/replaced using a very wide tip. First lift
the
outer legs, then idea is to spread the heat evenly across the entire
tab/pad
area. wet the pad & tab with some kester "44" solder, then apply the
wide tip
in a manner that gives the most surface area contact, at the same time
grasp
one of the legs with needle nose pliers, the fet will come right off.
I keep some alcohol in a small dish to drop the fet in so it doesn't
stay hot &
possibly damage it (if I am not sure it's good).
To install a new fet, use the same wide tip & wick the pad very clean,
then
wet the pad with a very thin coat of silver based solder, let the pad
cool,
align the new fet & tack the legs to hold it as aligned as possible, now
heat
the pad & re-wet while using a wooden dowel to apply slight pressure to
the new
fet, as soon as you see complete flow & the fet sinks into position,
remove the
heat, hold the fet for a few seconds then use an alcohol soaked q-tip to
cool
the fet.
I replaced a lot of these fets before I was able to make it look good.

Sunny