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I Did It. You Can, Too ! SMD Circuit Board Repair

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  • I Did It. You Can, Too ! SMD Circuit Board Repair

    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 ...





    .

  • #2
    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.
    Location- Rugby, Warwickshire. UK

    Comment


    • #3
      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..
      Last edited by Lew Hartswick; 05-07-2015, 06:44 PM.

      Comment


      • #4
        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

        Comment


        • #5
          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 !
          Gary


          Appearance is Everything...

          Comment


          • #6
            Originally posted by Lew Hartswick View Post
            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.

            Originally posted by Lew Hartswick
            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.

            .

            Comment


            • #7
              Originally posted by Lew Hartswick View Post
              How did you get it open.??
              ...lew...
              Butter knife or wide flat piece of steel of appropriate thickness to wedge the halves apart.

              Comment


              • #8
                Originally posted by goose View Post
                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
                A Weller WESD51 with a 1/16" tip (#ETA) adjusted for 471؛F.

                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.


                .

                Comment


                • #9
                  Originally posted by Mark Rand View Post
                  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.

                  .

                  Comment


                  • #10
                    Originally posted by Rosco-P View Post
                    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.

                    .

                    Comment


                    • #11
                      Originally posted by EddyCurr View Post
                      Umm, the rectangular notch takes the edge of a house key
                      nicely.

                      .
                      Whatever works. No big thing.

                      Comment


                      • #12
                        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) :>()

                        Comment


                        • #13
                          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!

                          Comment


                          • #14
                            Originally posted by EddyCurr View Post
                            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.

                            .

                            Comment


                            • #15
                              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.



                              Originally posted by EddyCurr View Post
                              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 A.

                              Make it fit.
                              You can't win and there is a penalty for trying!

                              Comment

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