Made By Monkeys

What you need is solder with 37% lead in it!

Thanks to this entry and the comments on the linked Design News site I've been encouraged to open up my old Ford key fob, which has just failed, and found exactly the same problem.

Three comments, though:

• after ten years hard use, failure of just one switch in the three on the board is probably acceptable;
• given that the assembly is double-sided surface-mount, through-hole components would be hard to design in and more costly to produce;
• some reduction in the incidence of this particular failure mechanism might be produced by choosing a finish other than ENIG.

Of course a totally different approach to the problem (like using capacitative sensors), which would remove mechanical components altogether, might be even better. Or we could think out of the box and persuade car manufacturers to use standardised parts rather than roll their own!

Glad we've been of some help, Martin, and thanks for some good points. I'm sure cost is an overriding factor.

About the switch, does ten years use, even hard use, make failure acceptable? That's a question we could open out. I feel a Poll coming on... How could we phrase it? After how many years use does switch failure become acceptable? 1, 2, 5, 10, 12?

Suggestions welcome for phrasing such a poll.

Headphone sockets in personal music players frequently suffer the same fate, for much the same causes I imagine.

If the switch rear sat flat on the pcb it would reduce stress on the legs - it looks like it might have a gap under it from the photo. However, looking at the pads before re-tinning I would say it was never soldered properly in the first place - contaminated switch pins?

Dave

I suspect that there may be a very slight gap under the switch, to allow for a glue spot, which is sometimes used in PCB manufacture.

If there is indeed a gap between the switch and the PCB then there'd be a tendancy for the legs to splay out sideways if the button is pushed really hard, stressing the solder joints and leading to premature failure. RoHS solder probably doesn't help either..

How many people when faced with a remote control or key fob that won't work simply press the button harder and harder in the hope that something will happen? I know I do!

Maybe the answer is to educate car owners in the proper use of their key fobs...?

;)

Dave

(PS: The "Dave Hill" above isn't me..)

Ah there we are. This is no doubt a 'feature' built into new cars. Never mind the switch, its the captive owners, a phrase coined by modern marketeers, once know in engineering circles a Captive nuts. I digress, with the bailing out of the auto industry, the bean counter management needed to see source of income from engineering to stave off bankruptcy.

This is it - £250 for the non technically literate man in the street.

I think there may be more than an element of truth to what you say, Alex. However, that "income source" was needed even before the current crunch...

I was handed one of these from a volvo some years ago, probably over ten years old, but the switch itself had worn out! After 10 years a lot can go wrong!