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Vintage threads from the first ten years

Re: reworking

6/4/2000 2:29 AM
Daniel R. Haney	Re: reworking Zachary Vex wrote: > reworking double-sided boards can be a real > challenge. the plated-thru holes are very > difficult to clear on a multi-pin component > and you do more damage with the excess heat > from multiple tries than you would on a > single-sided board. Hiya, Zach. Reworking PCB's non-destructively was/is so important that I bought an old industrial desolderer for $50 and a $135 air compressor to power it. Had I looked harder, one with a self-contained vacuum pump could have been had for $140 total. With an antique Pace Ped-a-Vac III, I can desolder 16-pin DIP components, tap the board a few times and watch the chip fall out without touching it. Plunger solder suckers and desoldering wick can't do that. If you want to rework boards with success and reliability, you use an industrial desolderer. This is not snobbery. Once you've used one, you know it's the correct tool, especially if board rework is part of your business. Anything less simply sucks and not very well, either. -drh --

6/4/2000 2:29 AM

Daniel R. Haney

Re: reworking

Zachary Vex wrote:

> reworking double-sided boards can be a real
> challenge. the plated-thru holes are very
> difficult to clear on a multi-pin component
> and you do more damage with the excess heat
> from multiple tries than you would on a
> single-sided board.

Hiya, Zach.

Reworking PCB's non-destructively was/is so important that I bought an old industrial desolderer for $50 and a $135 air compressor to power it. Had I looked harder, one with a self-contained vacuum pump could have been had for $140 total.

With an antique Pace Ped-a-Vac III, I can desolder 16-pin DIP components, tap the board a few times and watch the chip fall out without touching it. Plunger solder suckers and desoldering wick can't do that.

If you want to rework boards with success and reliability, you use an industrial desolderer. This is not snobbery. Once you've used one, you know it's the correct tool, especially if board rework is part of your business.

Anything less simply sucks and not very well, either.

-drh
--

6/4/2000 5:02 PM

John Greene

Re: PCB Manufacture

quote:
"Two-layer boards are an ambitious undertaking
for hobbyists."

I don't think so. I do it all the time.

quote:
"You have faith that the layers line up because to
put registration marks on the top and bottom side
resist patterns and lined them up as best you could."

No a problem, 'specially with small boards. Assuming the photo-etch process that is. I just make a pocket with the top layer and bottom layer transparency and put the board inbetween. Registration has never been a problem.

quote:
"As you said, commercially-bought eyelets are pressed
into pads to connect the layers."

Too much trouble, I just solder a piece of resistor lead between the layers.

quote:
"Commercial PCB fabricators plate the copper through
the holes. This anchors a solder pad to the board
and permits reworking the board with minimal damage."

twoo.

quote:
"Two-sided boards with plate-through holes don't sound any better than single-sided ones, but
they are a lot more rugged."

I like it better as I make the top layer (assuming leaded parts) the ground plane. Makes routing traces a lot easier without having to worry about getting ground everywhere. As far as reworking, I only solder on the side the connection is being made.

just my $.02

--johng

6/4/2000 8:24 PM
Daniel R. Haney	John, These comments pertain to commercial circuit boards. My experience in reworking boards is that the 2-sided critturs will withstand a few more desolder-solder cycles than the 1-sided ones. Commercial fabricators often plate the traces up to 1.5 oz. thickness before applying the resist mask for final etching. Thick traces are more rugged and less likely to burn off. The worst boards, IMO, are from old Electro-Harmonix and Way Huge, both single sided. E-H did it as cheaply as possible; they scrimped on both parts quality and board quality. Way Huge had good quality parts but fragile fine traces on a thin flexible fiberglass board. Neither E-H nor WH boards withstand much heat in reworking. You ALWAYS burn off a pad, even with a good temperature controlled desolderer. In stark contrast, Ibanez boards, though 1-sided, are rugged enough for a half dozen rework cycles. They use mediocre parts but make a solid PCB. Go figure. For these reasons, I say that a commercial 2-sided PCB with plate-through holes is less fuss to rework. -drh --

6/4/2000 8:24 PM

Daniel R. Haney

John,

These comments pertain to commercial circuit boards.

My experience in reworking boards is that the 2-sided critturs will withstand a few more desolder-solder cycles than the 1-sided ones.

Commercial fabricators often plate the traces up to 1.5 oz. thickness before applying the resist mask for final etching. Thick traces are more rugged and less likely to burn off.

The worst boards, IMO, are from old Electro-Harmonix and Way Huge, both single sided. E-H did it as cheaply as possible; they scrimped on both parts quality and board quality. Way Huge had good quality parts but fragile fine traces on a thin flexible fiberglass board.

Neither E-H nor WH boards withstand much heat in reworking. You ALWAYS burn off a pad, even with a good temperature controlled desolderer. In stark contrast, Ibanez boards, though 1-sided, are rugged enough for a half dozen rework cycles. They use mediocre parts but make a solid PCB. Go figure.

For these reasons, I say that a commercial 2-sided
PCB with plate-through holes is less fuss to rework.

-drh
--

6/5/2000 12:32 AM
John Greene	Pardon my confusion but you mentioned registration marks for lining things up and 2 layer boards being an ambitious undertaking for the hobbiest. And the title of the thread is PCB Manufacture. I assumed we were talking about making boards.... My mistake. I found with the proper attention to heat, solderwick works really well for me. Just don't dwell in one place too long. And if you don't get it clean the first time, add solder and try again. Personally, I've sucked up more pads with a desoldering station than I have lifted with solderwick. --johng

6/5/2000 12:32 AM

John Greene

Pardon my confusion but you mentioned registration marks for lining things up and 2 layer boards being an ambitious undertaking for the hobbiest. And the title of the thread is PCB Manufacture. I assumed we were talking about making boards....

My mistake.

I found with the proper attention to heat, solderwick works really well for me. Just don't dwell in one place too long. And if you don't get it clean the first time, add solder and try again. Personally, I've sucked up more pads with a desoldering station than I have lifted with solderwick.

--johng

6/5/2000 2:18 AM
Daniel R. Haney	John, Apologies first -- The archness in my last response was unintended. At the time of writing, it was only a dry narrative of things of things screwed up in the past vs. things that worked (or so I'd thought). No offense intended. > Pardon my confusion but you mentioned registration > marks for lining things up and 2 layer boards > being an ambitious undertaking for the hobbiest. We-e-e-ell, it _was_ ambitious the first few times I tried it back in...uh...a long time ago. Rub-on traces were pretty tedious back then but photo-positive is a blessed relief. I still have to retouch laser printer transparencies with a Sharpie pen. If you do double-sided boards all the time with good success, then that to me is a reflection of your skill at something fraught with opportunity for mistakes. Sometimes I think life is too short to spend hours in front of a drill press with an aging thrust bearing while trying to get a few more straight holes through the board. q(I found with the proper attention to heat, solderwick works really well for me. Just don't dwell in one place too long.) This is good advice for _any_ board rework. I use solder wick to clean out larger components like jacks, switches, pots, but precisely because I _can_ linger on something with larger pads around it. q( And if you don't get it clean the first time, add solder and try again.) Yeh. Also, a little solder flux helps on old joints that have turned dull gray. q(Personally, I've sucked up more pads with a desoldering station than I have lifted with solderwick.) Not to sound intransigent, my experience is exactly the opposite. A preference is for devices that suck isn't a perverted choice, is it? ;^) -drh --

6/5/2000 2:18 AM

Daniel R. Haney

John,

Apologies first --

The archness in my last response was unintended.
At the time of writing, it was only a dry narrative of things of things screwed up in the past vs. things that worked (or so I'd thought). No offense intended.

> Pardon my confusion but you mentioned registration > marks for lining things up and 2 layer boards
> being an ambitious undertaking for the hobbiest.

We-e-e-ell, it _was_ ambitious the first few times
I tried it back in...uh...a long time ago. Rub-on
traces were pretty tedious back then but photo-positive is a blessed relief. I still have to retouch laser printer transparencies with a Sharpie pen.

If you do double-sided boards all the time with good
success, then that to me is a reflection of your
skill at something fraught with opportunity for mistakes.

Sometimes I think life is too short to spend hours in front of a drill press with an aging thrust bearing while trying to get a few more straight holes through the board.

q(I found with the proper attention to heat, solderwick works really well for me. Just don't dwell in one place too long.)

This is good advice for _any_ board rework.
I use solder wick to clean out larger components
like jacks, switches, pots, but precisely because I _can_ linger on something with larger pads around it.

q( And if you don't get it clean the first time, add solder and try again.)

Yeh. Also, a little solder flux helps on old joints that have turned dull gray.

q(Personally, I've sucked up more pads with a desoldering station than I have lifted with solderwick.)

Not to sound intransigent, my experience is exactly the opposite. A preference is for devices that suck isn't a perverted choice, is it? ;^)

-drh
--

6/5/2000 3:33 AM

John Greene

quote:
"Not to sound intransigent, my experience is exactly the opposite. A preference is for devices that suck isn't a perverted choice, is it? ;^)
"

heh, you're funny.

Actually, now that I think about it, it's my own problem. When I use a desoldering station I can't help but move the end of the tip in circles around the pin to make sure I get all the solder. This, more times than not, lifts the pad. I just can't seem to get myself to not do it though! So, consequently, solderwick works better for me.

quote:
"Yeh. Also, a little solder flux helps on old joints that have turned dull gray.
"

commenting on your old age here or a rework technique? ;^)

--johng

6/5/2000 5:15 AM

Daniel R. Haney

John Greene wrote:

quote:
"When I use a desoldering station I can't help but move the end of the tip in circles around the pin to make sure I get all the solder. This, more times than not, lifts the pad."

Using solder wick, I often trash the pads because the iron isn't powerful enough. 25 watts don't do it. A bigger iron with more thermal mass is what I really need.

To plod on doggedly to the boredom of all present, this desolderer technique works for me:

Apply the extractor tip *gently* to the pin and wait until the solder melts, circle the pin 3-4 times in no longer than 1.5 seconds.

Three recurrent gotchas are too high a heat setting, clogged filters, and a rough eroded tip.

The first two are ordinary adjustments/maintenance; the tip can be polished when rough.

For through-hole desoldering, the vacuum should be about -15" Hg minimum, but -20" is better. For surface mount work, -10" to -12" Hg vacuum is enough.

In older desolderers, the vacuum pump may be worn and weak, as is very common in PACE or APE units having a rotary vane pump. You can refurb them by polishing the vacuum chamber then adjusting the rotor-chamber clearance to .01". All you need are 600# sandpaper, screwdrivers, and a Dremel rotary hand toool.

-drh
--

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