A Dog’s RF Tag Fails – Is RoHS the Culprit?

barney-georgia-card.jpg Over two million pets in the UK have an idENTICHIP RF tag in the scruff of their neck that works as a kind of electronic ID tag. So what are the chances that two new devices based on the same technology — which has had a good track record up until now — would fail in three different dogs (including Barney, shown here with his pal Georgia, who coincidentally lives next door to one of the other dogs). And then to have those same devices weirdly and spontaneously rectify themselves after “xray”‘ investigations? The odds must be, well, big enough to be almost impossible.

And that got Barney’s owner, an engineer named Roger Unwin who works in the electroncis industry, wondering if by chance the device maker was caught up in unintended consequences of the new lead free regulations for the electronics industry? Could it perhaps have started using lead-free solder — in compliance with RoHS regulations that went into effect in July 2007 — for any of the connections on the miniature device? If that were the case (which the manufacturer ultimately did confirm), he speculates that tin whiskers could well be to blame for the problem. The subject of tin whiskers has been a source of controversy in the design engineering community, with blogs and forums frantically abuzz on the topic noisily on the topic, as evident in the popular Pushback, an anti-lead-free site. “If the xray process used to locate the devices works by emitting electrical / EMF energy it might have been sufficient to destroy a whisker in a similar way to a fuse blowing,” says Unwin. Barney got lucky. Unwin’s vet initially indicated that the failed chip might have to be removed but after further investigations the vet discovered a second could abe implanted and did it FOC. The neighbor’s dog, Algie, was a less fortunate — she was impounded by authorities when her chip failed to work and had to endure a procedure to remove the failed chip. A third dog, Coco, who lives 20 miles away from the other two also came up with a failed chip. Only poor Coco was impounded in Calais, France by authorities when her chip failed.

Related Tech News

2 Comments

  1. ron burgess
    July 17, 2009 20:43

    I became aware of tin wiskers about 30 years ago when I had some repeated obscure problems with a synthesiser on a particular model of an airbourne DME which was shielded by tin plate covers,and during troubleshooting the fault it was found that parts of the circuit had a low resistance to other parts of the circuit, to clear the problem of unlocking proved to be a permanent cure by thorough cleaning the pcb assy and covers, it was then noticed on one occasion that there were very fine hair like whiskers protuding from the tin plate cover and linking down to the pcb and IC’s etc. which had a resistance of about 200 ohms and were up to a half inch long, the problem was never repeated on the same unit since.

  2. Alan Melia
    July 15, 2009 12:52

    I remember coming across tin wiskers about 40 years ago, and finding silver even worse. My investigations at the time suggested that only pure tin grows wiskers and even a small amount of another metal in the alloy severely depresses the tendency to grow wiskers. I have a picture somewhere I took of what I assumed to be a silver wisker( we never had time to analyse it) which must have been over 1 inch long. We were advised by materials chemists it would have been accelerated by a sulphur-rich atmosphere (possibly due to the degradation of rubber covered cable, silver plated BNC connectors were black) the devices in question were TI epoxy encapsulated op-amps, which “latched up”. Brushing the board with a paint brush cleared the problem, but was not acceptable on remote telemtry stations. A change of device to one with a solder dipped ( in the 60/40 days) lead-frame was made and the problem went away.
    I would like to see some definitive tests on high-tin lead-free solder to deteremine whether it does actually form the “anecdotal” wiskers. If so how much and what additive needs to be used to supress them. Until then I am dubious of the “convenient scapegoat”. Surface films can be grown in damp conditions which show the same effect.

Share your knowledge - Leave a comment