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View Full Version : I Did It. You Can, Too ! SMD Circuit Board Repair



EddyCurr
05-07-2015, 05:08 PM
In-laws (fixed-income seniors) reported that both key fobs
for one car were no longer functioning.

A quote from the dealer of C$250 apiece, plus labour
rocked them. My search online for third-party sources
indicated that pickings were slim and vendors were sketchy.
Opening the cases revealed that the Unlock microswitch
(SW2) had become desoldered and the Lock switch (SW1)
joints were showing signs of fracture on both fobs.

While I have soldered up a few perforated boards, I had
never put an iron to a surface mount board. The concern
was that careless heat could desolder adjacent items or
damage the far smaller components used for SMD boards.

With nothing to lose, however ...


http://www.slalom4me.com/imaged_a01/jpg/other/misc/2015.05.06_SubaruFob_01.jpg

http://www.slalom4me.com/imaged_a01/jpg/other/misc/2015.05.06_SubaruFob_02.jpg

http://www.slalom4me.com/imaged_a01/jpg/other/misc/2015.05.06_SubaruFob_03.jpg

.

Mark Rand
05-07-2015, 05:32 PM
I've managed a the same sort of repair on exactly the same sort of device (A Renault key fob). I now have a bag of surface mount push button switches because the minimum order for the one I wanted was 25, but it was still far cheaper than a replacement key.

It seems to me that it's always the switches that fail and the replacement costs for the keys are larcenous.

Lew Hartswick
05-07-2015, 05:41 PM
I have a pair like that with the extra sw for the tailgate, I see the place for it on your board. How did you get it open.?? I have to start a file on Subaru repairs now somewhere
in the computer.
...lew...
ps how long does the cell "battery" last in one of those? mine has been going for about 6 or 7 years now.
..lew..

Joe Rogers
05-07-2015, 06:02 PM
If it is the 2032 our shop sees 6 or 7 years with normal button presses.
YMMV but I'd get a new battery and get ready to install it.
Joe

goose
05-07-2015, 06:48 PM
What kind of soldering iron did you use, and did you apply any solder or just give the board a quick touch with the tip ?

Well done !

EddyCurr
05-07-2015, 06:58 PM
How did you get it open.??Above the Lock symbol, on the perimeter there is a rectangular
notch along the seam. Insert a suitable object (edge of head of
a house key, screwdriver blade ...) and gently twist. The case
can be split for battery replacement without having to remove
it from a key ring.


how long does the cell "battery" last in one of those?I have reason to believe the batteries in these were OEM. The
vehicle was purchased late in '05, so that pegs service life to
date at 9-1/2 yrs. They are CR2025 3V lithium cells. I changed
them on spec.

.

Rosco-P
05-07-2015, 07:14 PM
How did you get it open.??
...lew...

Butter knife or wide flat piece of steel of appropriate thickness to wedge the halves apart.

EddyCurr
05-07-2015, 08:18 PM
What kind of soldering iron did you use, and did you apply any
solder or just give the board a quick touch with the tipA Weller WESD51 (http://www.testequipmentdepot.com/weller/solder/wesd51.htm) with a 1/16" tip (#ETA) adjusted for 471F.

Before someone cries 'foul', let me say that while features of
the WESD51 gave me confidence to try my hand; after the fact,
I am convinced that my 15W Radio Shack 64-2051 iron would do
the job equally well. (The 48W tip on one of my Ungar irons might
cause trouble, though.)

Several online resources offered tips for tackling the job. These
suggested 0.015" 60/40 or 63/37 eutectic solder. The smallest
I could find locally was 0.025", but I returned this afterward. The
online suggestions were to apply solder to the tip, then apply tip
to the traces - didn't need skinny solder to do that.

The SW2 (Unlock) switches for both fobs were completely separate
from their boards and loose under the rubber water shield. I used
rosin and desolder braid to lift OEM solder, then tinned the pads
on the boards and switches. The switch was held in place while
one pad on one side was 'tacked' to hold the unit in place, an
adjustment was made for final position, the opposite side traces
soldered, then the second trace on the initial side was completed.

The SW1 (Lock) switches were still in place, but showed fractured
solder traces. Rosin and desolder braid was applied, followed by
a dot of solder on the tip for each of the four trace/pads.

Very little rosin was applied. Still, Rosin Remover was sprayed on
Q-Tips and these were used to wipe around the switches.

Suggestions:

Search out online resources on the subject of hand-soldering
SMD boards.
Refrain from drinking coffee beforehand. I didn't and had
a case of the jitters that normally would have gone unnoticed,
but which were quite apparent while trying to apply tip to pad.
Clear the workspace and surrounding floor to give yourself
a fighting chance of finding a switch if it gets away from you.
Work in strong light.
Use vision aids if possible. If nearsighted like me, remove
eye glasses and wear clean safety glasses. (I also used 4X
power 2-1/2" focus watchmaker's loupe.) Otherwise, a magnifier
headband like the Bausch-Lomb MagnaVisor may help.
Consider wearing a P100-rated filter mask (aka: respirator).
The smoke from soldering ALWAYS goes to your face & up
your nose.

.

EddyCurr
05-07-2015, 08:33 PM
It seems to me that it's always the switches that fail and the replacement
costs for the keys are larcenous.The replacement key fob prices are impossible to justify. What's
more, Canadian dealer prices are in the vicinity of twice the already
high US prices.

All the switches on these fobs were functioning. IMO, the sluggish
& inconsistent TX/RX performance, together with the leverage of the
exterior push buttons lead to abuse of the small solder joints holding
switch to board. Didn't lock/unlock with the first push? Hit the button
harder next time and again for good measure!

Incidently, the heat resistance of the white case of the switches
surprised me. I actually held the tip of the iron to the case to see
whether it would deform/melt. It probably will, but at more heat
applied longer than is necessary for adequate soldering.

.

EddyCurr
05-07-2015, 08:37 PM
Butter knife or wide flat piece of steel of appropriate
thickness to wedge the halves apart.Umm, the rectangular notch takes the edge of a house key
nicely.

.

Rosco-P
05-07-2015, 08:54 PM
Umm, the rectangular notch takes the edge of a house key
nicely.

.

Whatever works. No big thing.

Juiceclone
05-07-2015, 10:20 PM
following clues on the net, I understand that these types of boards can be re soldered by heating them in a toaster oven ...carefully at a very tightly controlled heat for a short time. .
..As long as there are no electrolytic capacitors present as I discovered...they explode nicely...(not to be tried when the wife's home) :>()

CalM
05-07-2015, 11:17 PM
I've a binocular microscope on the bench for just such work. That or the "visor vue" magnifiers.

A tight wrap of bare copper builders wire (14 ga) with a "stinger" works to give a fine point.

The problems I've had usually revolve around errant hot tips around , but not in, a limited field of view.

Good eyes would be such a boone!

EddyCurr
05-08-2015, 01:08 AM
Suggestions:
Consider wearing a P100-rated filter mask (aka: respirator).
The smoke from soldering ALWAYS goes to your face & up
your nose.Further review suggests that an N95 or N99 filter might
be a better choice for soldering.

.

Paul Alciatore
05-08-2015, 01:31 AM
Well, as far as the switch always being the point of failure, is that any surprise? There are only two moving parts and the switch is a lot smaller and more delicate than the button that activates it.

On the heat resistance of the white case, it is probably teflon or a similar high temperature plastic or perhaps even a ceramic. They have to be able to withstand the heat of an oven when the factory solders them. They put a solder mask on the board and wipe solder paste (solder powder and flux) over it so it is left on the component pads on the board. The mask is removed and the parts are placed on the board, on top of the solder paste. Another, solder resistant mask may be used to hold them in place. Then it all goes into the oven for a heat cycle. They do not use soldering irons. The whole thing with all parts is heated to the melting temperature of the solder, which with lead free solder is usually higher than the older lead types. Around 360 to 400 degrees F. It is held at this temperature for a half minute or so, with ramp up and ramp down time before and after that to insure complete penetration of the heat and proper cooling time.

As for the price, in the quantities that the auto companies order, they can probably make them or have them made for a dollar or less. The rest is pure profit. And greed. Looks like a business opportunity to me. Those switches, that last more than 5 or 10 years, probably cost the fob makers about $0.01 or less each.




The replacement key fob prices are impossible to justify. What's
more, Canadian dealer prices are in the vicinity of twice the already
high US prices.

All the switches on these fobs were functioning. IMO, the sluggish
& inconsistent TX/RX performance, together with the leverage of the
exterior push buttons lead to abuse of the small solder joints holding
switch to board. Didn't lock/unlock with the first push? Hit the button
harder next time and again for good measure!

Incidently, the heat resistance of the white case of the switches
surprised me. I actually held the tip of the iron to the case to see
whether it would deform/melt. It probably will, but at more heat
applied longer than is necessary for adequate soldering.

.

Paul Alciatore
05-08-2015, 01:52 AM
Oh, there are many, MANY instructional pages and videos on the web for soldering surface mount components. Just do a search for them. Some of the favorite tools are toaster ovens (I use one with a burnt out coil) and electric skillets.

I also made a hot air soldering tool from a Radio Shack de-soldering iron and an aquarium pump. It works great for repair work. I use it with an unmodified cup warmer to preheat the board.

http://www.piclist.com/techref/hotairpencil20usd.htm

macona
05-08-2015, 02:08 AM
At work I am usually modifying or repairing boards that are almost all SMT and the boards I design are all SMT as well. Little buggers too, most resistors and caps are 0402 which are .040"x.020". I am using an analog switch IC in one design and the one I found is a 8 pin chip 1.4mm on a side. Fun...

Juiceclone
05-08-2015, 08:40 AM
WOW I like that re-purpose of the solder sucker. I will keep that in mind the next time a board develops "cold solder" joints. Thanks

A.K. Boomer
05-08-2015, 09:22 AM
Good job Eddy, It's nice to throw the parts people bean counters a left curve most of the time --- those things are designed to fail after so many cycles and according to predicted statistics you were supposed to have already walked into the door and paid them 500 bucks... Sorry Subie, there's just some people you can't count on for that, deal with it...
I just repaired a toyota highlander driver side window door lock circuit board - dealer cost $568.00

It is ALWAYS worth the time taking a peek - get yourself a great magnifying glass and take a break in a brightly lit room and go over it with a fine tooth comb...

so many times it's a soldered joint and you do not even have to replace anything,,,

two biggest reasons its the soldered joint is either direct repetitive pressures being applied OR just a circuit that deals with a fair amount of heat at the joint depending what it's soldered too,
these heating and cooling cycles will work the attachment loose...

a quick heat up re-blends everything back together again and it's as good as new, which remember was not very good,
so add some beef up solder, now you not only have more strength - you also have more thermal mass at the area so if it was heat related you have a little better dissipation do to the extra surface area... it won't get quite as hot and it will be stronger to boot...

To all those engineers who pre-plan failures into parts - you have no idea who your up against... :cool:

wierdscience
05-08-2015, 10:39 AM
Good for you! I never really liked the fobs since once they quit it's either buy new or tolerate a useless appendage on the keychain.Thanks for showing us the way.

I wonder how much those things cost the mfgs versus how much they charge,$5 ? Especially those infernal chipped keys.

A.K. Boomer
05-08-2015, 10:44 AM
I wonder how much those things cost the mfgs versus how much they charge,$5 ? Especially those infernal chipped keys.

Just because they know they "got ya" or think they got ya :p

EddyCurr
05-08-2015, 10:53 AM
An oversight I thought about last evening is Electrostatic
Discharge. Inexperience and a climate where ESD is not as
much an issue as it might be for you led me to neither take
precautions from damaging components, nor caution about ESD
earlier in this thread.

Ground yourself and your tools when working with electronic
components.

CalM. That's a neat, uhm, 'tip' about adding a wrap of
14 ga copper around the business end of a soldering iron
and extending one end out to form a small soldering point.

Paul, thanks for the overview for oven soldering of SMD.
I have an abstract idea about how wave soldering works,
but plan to flesh that out a bit with some research, too.

I looked briefly to see whether the desoldering tip on the
iron in your link was available alone - the body of the iron
looks like a generic Ungar. Could just make one. Variable
temp control would be a benefit, but I seem to recall that
my WESD51 iron has some tip considerations due to the digital
controller feedback requirements.


I am using an analog switch IC in one design and
the one I found is a 8 pin chip 1.4mm on a side.That has to be approaching the point where the scanning
microscope is brought into play!

I'll take this opportunity to say that it is contributions
on activities out on/beyond the boundaries from folks like
yourself, macona, which prompt others such as myself to
have a go at something beyond our comfort zones.

The switches on these key fob boards were a good first project,
in part because they are somewhat isolated from other components.
I still managed to get a little too close for comfort to one
resistor. Less coffee and a Panavise-equivalent to hold the
board next time.

.

Fasttrack
05-08-2015, 11:49 AM
At work I am usually modifying or repairing boards that are almost all SMT and the boards I design are all SMT as well. Little buggers too, most resistors and caps are 0402 which are .040"x.020". I am using an analog switch IC in one design and the one I found is a 8 pin chip 1.4mm on a side. Fun...

Ditto. That board seems to be all 0603 and bigger except for two 0402 caps. That's big!

Last board I reworked was 2" by 3" and had 10 layers with a bunch of 01005 and 0201s on it. Without an aid, I can barely see the 01005s. I will hand place and solder 0201 without a magnifier but that's about my limit.

Paul Alciatore
05-08-2015, 02:41 PM
If you have a circuit board with surface mount devices and suspect bad solder joints, you can just CAREFULLY place it in a toaster oven and set the temperature to about 250 degrees. Allow it to warm up for about 3 or 4 minutes. Time for everything to come up to that temperature. Then crank it up to 400 or 450 and leave it there for about 1.5 to 2 minutes. Then turn it off. DO not disturb it for at least 10 minutes so all the solder can cool and solidify again. Don't open the door. Don't jar the oven. DO NOT TOUCH in any way. It does not take much to knock one of those tiny parts, that are measured in thousandths, out of place.

If your board has parts on both sides you will need some short supports (1/8" to 1/4") so that no parts are in contact with the oven tray or rack. If the board is resting on them, they WILL be moved around and that is bad, bad, bad. Put the side with the smallest parts down. And keep the board horizontal: do not position it vertical as the parts may slide down.

This is probably a lot safer way to re-flow the solder than using any iron. It probably isn't, but if you really think that additional solder is needed you can dab just a bit of solder paste next to the joint with a toothpick or other small tool. Go very sparingly: an amount equal to the head of a pin is probably ten times too much. When it reaches temperature it will melt and be sucked into the joint.

I found a perforated tray for these toaster ovens at a local dollar store. The holes are around 5/16" in diameter. I like it as the hot air can circulate under the board more easily.

Oh, do not start to think that more time is better. It is not. You just need to bring it up to melting temperature in a gentle curve and then let it cool down with equal gentleness. The parts and the board are thin so the temperature inside them and between them will equalize fairly quickly so even pads in the middle of a component will reach melting temperature quickly.

J Tiers
05-08-2015, 08:03 PM
The toaster oven is FAR too "coarse" a tool for this.

All you need is a medium low power soldering iron, and tweezers, good ones with fine points, preferably curved. That and a "flux pen", preferably the "no clean" type.

Since you have a shop, you can MAKE tips for special purposes, such as unsoldering a whole side of an IC such as is on that board. I have them for doing that, for unsoldering 44 pin Atmel microprocessors, etc.

I find it perfectly do-able to remove and replace 44pin chips, and even some of those %$#@! QFN packages. It's one reason why I badgered the eye doctor to give me back my nearsightedness at the bottom of my glasses..... 6" focus.

We routinely do that sort of stuff at work on prototype units.

Once in a while we do use a made-for-the-purpose heat gun, but generally its a soldering iron that is used.

Good on the O.P. for getting it done. One in the eye for the throwaway society.

oldtiffie
05-08-2015, 08:43 PM
I really don't have that problem as my "key" need only stay in my pocket as it is a "proximity" device that only requires that I be within a certain (about 1 metre) distance of the front doors, the boot and/or the drivers seating position. I just press a button on any of them and the door/s lock/unlock as required and I just need to press the start/stop start button and the engine starts. Very handy.

The "key" that I normally keep in my pocket also has a range in excess of 50 metres to open/close doors.

I did ask the dealer about the cost of a new "key" and his advice was to use an existing working key (our "spare" with its "number" on an attached tag) to make a new one much cheaper than having to start by re-programming the car computer if an entire new key is required.

The risk and potential costs are all part of the risk of having and using the car - which I accepted when it was explained to me when I bought the car - a new top-of -the-range Mazda 3.

I also accept that in the event that if the car cannot be driven that it will have to be towed to my (or any) Mazda dealers premises to be repaired and that I will get a replacement/"courtesy" car to drive as I liked until I pick up my own car from repairs.

My "courtesy car" (when I had my car serviced) was a brand new (200 km on the "clock") Mazda 2 which my wife and I were every impressed with indeed and which will probably be our replacement car when we trade our current Mazda 3 "in" in say 10 years time.

For what its worth the Dealer checks and if necessary, replaced the batteries in the "fob" (pocket) "key" each time the car is in for its service.