The Repair of SMD Circuits.....

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Janitor Tzap
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The Repair of SMD Circuits.....

Post by Janitor Tzap » Sun Jun 01, 2008 3:26 pm

Now that the Electronics Industry is clearly going to Consumer Electronics that use all Surface Mount Devices.
Repair of these items has become some what of a nightmare.

I've spent far too many hours on just removing one component from a circuit board.
And sometimes damaging the solder pads.

When I was still getting in consumer electronics that still had through hole soldered components.
I could quickly remove the component from a circuit board in a minute or two.

I'm starting too look at Hot Air Removal Stations as the next step in trying to work with these SMD's.
That and Hot Tweezers.
I've looked at the "Quick Chip" removal paste.
But that gets expensive when you have use it continuously on a daily basis.

{Even the July N&V has an article on how to convert a Convection Oven into
a SMD Solder Re-flow Oven.}

I can see that VernGraner's "Outfit A Work Bench for $100 Challenge."
Is going to be hard to accomplish.


So, how many of you are in the same boat?
Are you going to hang in there and make the conversion too the SMD Repair Tools.
Or like my one friend who was in the Consumer Electronic Repair Business.
Closed his doors, and moved on to something else.


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Externet
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Post by Externet » Sun Jun 01, 2008 6:26 pm

Welcome to my world, everyday at my workplace. Production, production, production.
It is more technique than tools what takes to rework surface mount components, until you hit the wall with ball grid arrays, which take a $150K machine to replace them.
Working under a microscope is not an exceptional activity. It is daily rutine.

At a factory it can be done because
You have all the spare parts on hand,
You have all the equipment needed,
You have all the technical manuals,
You work with a reduced assortment of boards,
You must put to work that out-of-the-oven board that misbehaves,
You have to if you need to pay the rent. :smile:

Consumer products are futile to fix unless you do it for sport. Expensive equipment deserve investing more time and effort, as replacing an entire board may be too costly.

Look as an example at a PC mommyboard, look at the average time to troubleshoot and repair, look at parts search and availability, look at service manual procurement, look at the salaries needed to survive, look at the replacement cost.

We are doomed. :sad: But... smile, tomorrow will be worse ! :grin:

Miguel
- Abolish the deciBel ! -

Robert Reed
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Post by Robert Reed » Sun Jun 01, 2008 6:48 pm

Just from a hobby point of view - when the thru hole components finally dry up, I'm gone! But that may take a few years and some manufacturing is still done thru hole today. I find no joy in working in that micro minature world and if I did I would have taken up "watch making " years ago.

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Dave Dixon
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Post by Dave Dixon » Mon Jun 02, 2008 4:53 am

I use QuickChip quite often, and agree that it is really expensive. If you didn't know - you can re-use it over and over. As soon as I lift an IC off the board, I do the old "sharp tap on the bench" trick, and retain the alloy for further use. It gets weaker as it bonds to the normal solder, but can be used several times! Just my two cents worth, Dave

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Post by Janitor Tzap » Mon Jun 02, 2008 10:27 am

It is more technique than tools what takes to rework surface mount components, until you hit the wall with ball grid arrays, which take a $150K machine to replace them.
Working under a microscope is not an exceptional activity. It is daily routine.
Ball Grid Arrays; are those like the PC board with the resistors and capacitors embedded into them?
If it is.....
God Do I Really Hate Them!!!!
Had a AKAI Tape Deck like that, that came in for repair.
The guy dropped it, and cracked the main PC Board.
The crack went through several resistors and capacitors.
I needed to get a schematic, because none of the embedded components were marked.
Plus, I couldn't use a soldering Iron.
The traces were to thin, and the heat would just remove it from the PC Board.
Thus, I used "Nickel Print" too paint onto the traces to re-make the connections.
{After I glued the PC board back together.}
As for the capacitors, and resistors.
Once I knew what the values were.
I got SMD's of the same value, and tacked them in place over the damaged resistor, or capacitor.
Then used the "Nickel Print" too paint the connections on to them.

As for use of a microscope.....
Yeah, I can relate to that.
While working at a TV/VCR Shop.
I spent hours at a time looking through a microscope at Tuner packs,
and main PC boards out of the newer Televisions & VCRs.
To save space; components were mounted on both sided of the PC Boards.
Or in many cases, a secondary board was mounted vertically onto the main board.
So, when operating the TV/VCR.
The combination of heat & cooling.
Plus, the weight of heavy components (Transformers & Large Capacitors).
Would cause the PC Board to warp, causing cracks, and open connections.
Some models were worse than others.
But after working on certain models.
You could pretty much guess what area you should look at first.
I use QuickChip quite often, and agree that it is really expensive. If you didn't know - you can re-use it over and over. As soon as I lift an IC off the board, I do the old "sharp tap on the bench" trick, and retain the alloy for further use. It gets weaker as it bonds to the normal solder, but can be used several times! Just my two cents worth, Dave
Yes, I've done that with the alloy.
But like you say; once the alloy is contaminated by the solder, and flux.
it quickly can't be used too many times more.

The "Sharp Tap" trick I've done with a heat gun on PC boards.
These were scrap boards that I wanted to get the sockets, or IC's off of.

A friend used a Blow Torch, but half the time he ended up burning the
components as well as the board.:lol:


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Don't fear SMDs

Post by philba » Mon Jun 02, 2008 11:37 am

It's not the end of the world. In fact, I like them a lot. I have a hot air station but don't need it for building with SMDs. I actually find building stuff with SMDs to be easier than with TH components. A lot easier. No cutting and shaping leads. You work on one side of the board (no flipping over). Desoldering is easy. The chips are easy to remove with hot air. Soldering is pretty quick: just put a tiny daub of solder on one pin, slide the chip on to it and when it solidifies, hit all the other pins with a little solder and you are done. Fast and easy. I just use a regular soldering iron for most. And if you make your own PCBs, no (or a lot less) drilling.

The biggest complaint I have is you wind up prototyping with PCBs. So I maintain a stock of TH components and use little adapter boards when necessary.

I only use a microscope a few times as my magnifying lamp is good for most things.

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Post by haklesup » Mon Jun 02, 2008 12:03 pm

Ball Grid Arrays; are those like the PC board with the resistors and capacitors embedded into them?
If it is.....
No its the square IC package with an array of tiny solder balls on the bottom, usually hunderds of contacts and they have to be soldered in a reflow oven at precise temperatures or you damage the package or board. BGA's come with balls spaced as closely as 0.5mm!

So far I have made due with a hot ari station, a fine tip solder station, a low mag microscope and some good tweezers. Add to that a solder sucker and yards of desoldering braid

Uaually I do not need to rework but just assemble small fixtures. That should change soon. My company is going out of Biz next week and we are selling the product lines and my job (and a few others) to another company who may want to go SMT with what we make.

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Post by MrAl » Mon Jun 02, 2008 2:48 pm

Hello,


SMD, the only three letter bad word.

I found out that soldering some SMD components is a three dimensional
problem, although at first it seems like only two. It looks like all
you have to do is align the pins with the pads and then solder, but
if one of the pins is bent even very slightly upwards, it doesnt touch
the pad like the other pins do and so it doesnt solder as nicely.
This happened to me when i went to solder a SSOP 28 pin device.
First, i was thinking about trying the 'dead bug' technique, and so
i tried soldering one small wire lead on one of the package pins
with the package upside down. That seemed like it might work, but
i changed my mind and thought that it would be better to solder this
to a PC board with the correct layout pattern, so i stopped doing that
and stuck it onto a proto board with the SSOP 28 pattern.
When i went to solder, most of the pins soldered ok i guess (although
wow they are close together and require a super steady hand)
but that one pin that i tried to dead bug solder was bent slightly
upwards because of the pressure from the soldering iron previously,
and this meant that the solder could not wick under the pin properly.
It meant that i had to try to 'bridge' the pin to the pad with solder.
Now normally i wouldnt do this, be we are talking a tiny tiny distance
here, from the bent pin to the board pad, and i didnt want to try to
bend the pin back for fear of pin breakage or package cracking or
something like that. In the end it worked, but it meant heating that
one pin for several seconds more than the others had to be heated.
That's not a good idea either. And keep in mind this was with only
one bent pin, i could imagine what a pain it would be if more pins
were bent like that (bent up less than the width of a human hair).

So the moral of the story i guess is that for very small packages like that
it's good to make sure the pins dont bend before you go to solder them
by keeping the part in the package until ready to use. Also, if you try
the dead bug soldering style you may not be able to mount that chip
to a board later on if you change your mind.

The 0.05 inch pitch parts are a little easier to deal with i guess.
The 5 lead devices dont seem too hard because there are so few
leads, but to try to unsolder the device and not kill it, that's another
problem. I ran into this problem a few years ago when i was thinking
of trying a different, higher current rated SMD transistor (only three leads)
but that meant basically that i had to destroy the previously soldered
(lower powered) transistor because removing it intact was not going to
be possible.

Also, there are some questions that come up when soldering these
packages by hand, such as the solder iron temperature profile.
Supposedly, if it's not close to exact the package develops leaks
between the pin metal and the package plastic, which means
contaminates get into the package over time.
I know lots of people do solder small packages by hand though
(even the SSOP type) and i guess they get long life, but then
again i never asked them how long a produce lasted when it has
been hand soldered (regular iron and regular small dia solder).

BTW, anyone ever try soldering or unsoldering an SMD part with
a heat gun? Perhaps with a special nozzle home built just for this?
LEDs vs Bulbs, LEDs are winning.

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Post by Janitor Tzap » Mon Jun 02, 2008 3:37 pm

haklesup wrote:
Ball Grid Arrays; are those like the PC board with the resistors and capacitors embedded into them?
If it is.....
No its the square IC package with an array of tiny solder balls on the bottom, usually hunderds of contacts and they have to be soldered in a reflow oven at precise temperatures or you damage the package or board. BGA's come with balls spaced as closely as 0.5mm!
YIKE'S!
Yeah, I've seen that style package, and thankfully haven't had to try to remove one!

As for soldering together the circuits.
Back when Heathkit still had stores around the country.
I got a few of their SMD trainer kits, and soldered them together.
But, these were simple one sided circuit boards.

The stuff that I've been seeing has components on both sides of the board.

Though, some of the computer mother boards that I've come across are multi-layer.
Which can have resistors, capacitors, even some diodes embedded into the PC main board.
{Were you can't get at them!}
Making repairing it almost impossible, if not impractical!


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Bob Scott
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Post by Bob Scott » Tue Jun 03, 2008 12:01 pm

Janitor: I am surprised if you are still trying to make a living in the consumer electronics repair business. All of the repair shops around here went out of business years ago. Consumer electronics is disposable now and is not built with any effort to make it repairable.

Al: The PCB rework techs at my old place of employment use hot air desoldering tools. The attachments are available for soldering stations in different shapes for different multi-pin packages.

Philba: Building prototypes is out of vogue now. The engineers use computer simulations instead. Then the design goes straight from schematic to layout and then to first article product for testing and tweaking.

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Janitor Tzap
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Post by Janitor Tzap » Tue Jun 03, 2008 4:32 pm

Bob Scott wrote:Janitor: I am surprised if you are still trying to make a living in the consumer electronics repair business. All of the repair shops around here went out of business years ago. Consumer electronics is disposable now and is not built with any effort to make it repairable.
Yes, I know :(
It's just frustrating that you can't repair the newer Consumer Electronic Items.
{At least not economically.}
The same as you once could with the older equipment.

Thou......
There are still some people out there that are bucking the trend.
I've found several sites that have people repairing, or offering support, or parts for some of the older electronics.
And as some here will a test.
Just because it's newer, doesn't aways make it better.:)


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Post by geb » Sat Jun 14, 2008 8:11 am

MrAl, you asked about using a hot air gun. I don't have a reflow oven, and I could not fix a USB wifi card that had suffered a heavy blow recently. The little board was damaged somewhere that could not be determined by meter or poking/prodding the smds. I threw it in the trash. Later that evening I took it out on a whim and heated the entire board with my milwaukee heat gun for about four seconds, just until the solder started to shine and flow.

Plugged it in. Whatdya know. Seems like it never worked better. I got pretty lucky I guess.

I suppose if you were working on a small area, or with small enough pcbs like this USB card uses, you might be able to place the probe of a digital cooking thermometer at some open spot on the board and thereby get pretty close to precisely the right target temp (>solder flow, <smd damage) before removing the hot air.

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Post by Lenp » Sun Jun 15, 2008 5:13 am

In my opinion...

I'm glad I'm into industrial controls where they still use a lot of sensors, switches and parts you can grab with a few fingers. Many years back I was into the consumer side, yeah, even way back to the days of point-to-point wiring and metal chassis. There were many excellent dealers in the area that had volumes of stock, tech data like Photofact's and smart support. All are gone now. Locally there are no parts suppliers except the near useless RS toy store emporium. The 'big brown truck' is my prime supplier now!

With todays hi-tech products, If you can get it apart, find a drawing, locate the bad part, and remove, it's still likely the part will not be available.

The best way to make money today in consumer electronics is to operate a landfill!

Len

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