Soldering Micro Components

Earl, too bad you glued the switch to the board. Most surface mount items have contacts that wrap up around their sides, at least part way. You just have to set the item over the pads and touch a fine point soldering iron to these side pads and they will melt the solder on the component as well as the board.

I have repaired quite a few this way.

Pete

I do this for a living.  Norton has the best approach.  It will be easest if you have solder paste ( tiny balls of solder in a suspension of flux) added to the solder areas.  If it truly is a BGA (ball grid array) part, then you may not be able to access the soldering areas .  We have machines that I program heat from the bottom to condition the board and part prior to solder.  The part is placed down over the contacts which have solder paste on them.  A nozzle blowing a programmed menu of hot air temps and air flows descends and heats the area up until the solder reflows.  In your case i would pre condition the area with heat from a hair dryer before using the solder iron.

I think I will try Norton's approach.  The epoxy was just between the body of the switch and the circuit board.  I am quite sure I can get the epoxy off with an Exacto knife.  I do remember the contacts wrapping around the sides.  

If that doesn't work, I will try to solder some long tiny diameter jumper wires between the circuit board and the switch.  Hopefully, there will still be enough clearance to reinstall the switch.  Although the switch had four contacts to solder to the board, it appears two were redundant and only two are required.

I am still puzzled why the switch fell off.  The solder joints appeared old.  I suspect that the switch has been loose for some time, possibly even from the date of manufacture.

Earl

One question regarding Norton's method.  How do I tell when the solder has melted since I won't be able to see beneath the switch?

Earl

Normally the pads on the board extend to the edge of the component beng placed there. I would add a drop of solder on each pad by either putting a small amount of solder on the iron or using the solder in paste that Steve suggests. When you put the component on the pads hold it in place with light pressure. As you heat the contact on the component you should see a fillet of solder form at the edge. Thats when you know its melted. Depending on what surrounds the switch you may actually be able to hold the iron at an angle where you can heat both contacts on one side at the same time. Normally these repairs are done with hot air, a heat gun with very narrow nozzle but the iron should work here.

Pete

Usually, there is at least a hint of the lead peeking out.  Also, if you put the solder on the pad for the contact, it should wick under and secure the lead.  I solder lots of SMT stuff on.

John,

Are you saying the solder should be placed on the metal tabs on the side of the switch rather than under the switch so the solder will wick towards the contact under the switch?  Actually I like that idea because the switch will probably not tilt during the soldering job, which might leave a gap under the remaining cold contacts.

It may be awhile before I can perform the repair as my grandson has the computer and he will probably wait until the current glue-job repair quits working.

Earl

There are a couple of possibilities on why the switch fell off.  One common cause is called Black Pad.  Some circuit board manufacturing processes if not properly controlled will cause this deterioration of the solder joint (similar to the zinc pest in the Lionel prewar parts).  You need to look at the pads you are going to solder to and make sure they are shiny.  If not then you need to remove the solder on the pads with solder wick and lightly scrape the remaining solder coating off until you get some orange looking copper showing through.  Not a complete removal of the solder but enough that you have a new surface to bond to.  If you have some tin/lead solder with rosin flux I would use that in this instance.  Then put some new solder on the contact pads with new solder using a soldering iron.  If your new solder lays down and has a very low profile of height then you should be okay.  If your new solder balls up on the switch contacts and will not lay down, then you need to remove that solder and do more scraping.  Once you get the solder coating down, then place and reflow your parts.  If your original failure is due to HIPS, then that is another mfg issue and redoing the solder joints with new solder will fix that.  Unfortunately you may have HIP joints on other components in the future.

AusSteve,

Thank you for both of your posts.  I obviously do not have the equipment you talked about in your first post, as I am just a hobbiest.

The solder on the circuit board was a medium to dart grey color and did not appear to be broken.  The solder was flat with the impression of the switch imbedded in it, so I assume it was either a bad solder job or it had the problem you described in your second post.  I will take your advice and get as much of the old solder off as I can.

Earl

I was going to suggest cleaning the contacts and some flux, preferably rosin based.  Earl, think of how you sweat copper pipe.  You clean the parts, apply flux, and then heat the joint.  When you apply solder to the edge of the connection, capillary action sucks the solder into the joint all around.  The same principal applies to these surface mount components.  Solder at the edge will wick right in and join them if they're clean parts.  Obviously, the flux helps.