Tin whiskers and other packaging problems

[Kalee20]

Very interesting. I used a few Lockfit transistors about 1979/1980, though on test equipment, not production products. Didn't see many after that...

So what was wrong with Lockfits that isn't a problem with the smaller TO92 package which was developed earlier? I would have thought, use the same techniques, just a larger moulding... More epoxy around everything should make a good thing better!

[Pat Pending]

So what was wrong with Lockfits that isn't a problem with the smaller TO92 

Later ones weren't so bad. But the earlier ones had no provision for bonding the quite large surface area of the leadouts to the packaging, was molded in two seperate opperations, was made from a hygroscopic plastic, and the transistor chip and interconnections were completely inbedded in the case material. The TO-92's had smaller (mostly) round leadouts that were sintered to provide bonding to the epoxy, were made from a more resin rich epoxy and were encapsulated in one opperation with a "void" for the silicon to live in. the lockfit was designed to provide the consumer electronics industry with a cheap easy to use package that would simplify assembly and speed up production, which it did, but the packaging was just that, cheap. BTW the ones in old hybrid TVs hardly ever used to fail, the valves kept them warm and dry! And post 75 were the improved ones. TFK Types were the ones to have, they hardly ever failed.
The gent I was talking to said that Mullard only ever made one good transistor package the glass SO2. Regards. Andy.

[Pat Pending]

Further to the question of reliability issues with semiconductors. What has to be bourn in mind is that once released to the market, and included  into some technical marvel outside the manufacturer's control, the reliability of that part is then at the mercy of the equipment designer, and the end user, my own experience that I recounted in the first post on this topic was proof positive of this. Take a transistor, that has the correct electrical specifications, and include it in your brainchild, then use that product in a hostile environment, outside the manufacturer's specs, and outside its manufacturing deficiency's, (sorry, but there is no such thing as perfect, only different levels of imperfection) and it will fail. Add further protection to the equipment at assembly (in my example tropicalization) and that part will possibly then be more reliable than including a better specified part in the first place (in my example TO-18 package transistors with the same specifications). The forgoing are amongst the reasons why semiconductor manufacturer's won't consider guarantee claims on devices that have been soldered in to equipment. As one sales guy from Fairchild Semiconductor said to me once, " Most of the data downloads that are done for our products are front page only." To keep things in perspective, (and to pick figures out of the air), if in 40 years the BC107 had an in service failure rate of 1/1000, and the BC147 had one of say, 20/1000, the BC147 has twenty times worse reliability than the BC107. But it also means that 980 BC147's are still working. Pessimism is a good personality trait in a design technician. Regards. Andy.

[Radio Fixer]

Thanks for an interesting thread and welcome to the Forum Pat.

Gary

[Mark Hennessy]

I agree - a most interesting thread indeed. The information here will enable me to make my transistor article more complete, so I am especially grateful

I was especially pleased to read about the later improvements to the package, which matches my experience of later Lockfit-equipped radios being generally more reliable.

So, thanks for this!

Mark

[Pat Pending]

Thanks all. Most of the info came from the Gent I referred to. He only lived a couple of hundred yards from us for twelve years, but I only got to know him a couple of months ago when I saw some cardboard boxes in a skip outside his house when he was about to move, that had a load of old valves in them (That's another story). I went to the door to ask about them, and found out that I had been living near this very knowledgeable and interesting chap, and had only swapped polite greeting when we had met walking the dogs! It's good to talk!

Garry. I notice you're from the Southend area. I used to deal with a company on the airport industrial estate called BK electronics. Never used to enjoy trying to get over the Army & Navy roundabout at Chelmsford during rush hour in an overloaded Transit, but there was always a friendly welcome and a cuppa waiting when I got there. Do they still exist, the last time I went to that neck of the woods it looked like they've built a new city on the road out past where Perrys garage is/was?

Thanks Mark. Glad to pass this on. I think the old proverb about understanding your past helps you plan your future, is a good reason to document these sorts of anecdotes. I noticed that the picture of the transistor didn' t come out to well, the original file was about 50 k, did I do something wrong on the upload?
Regards. Andy.

[westcliff]

Hello Pat, BK Electronics are still there.

http://www.bkelec.com/index.htm

Gus.

[Pat Pending]

Hello Pat, BK Electronics are still there.

http://www.bkelec.com/index.htm

Gus.

Hello Gus. Thanks. Wow just realised, its been the thick end of thirty years since I had dealings there, time flies. Love the avatar, a gold KB? custom restoration? Is it yours? Nice! Regards. Andy.

[Gingpeakin]

Fascinating topic...

A few years ago I had a couple of 2N something TO92 transistors fail in an HP5326B Counter-Timer-DVM. The first small signal transistors I had ever seen fail that hadn't been taken out by larger sibling. It was one of those faults that appeared after the unit had warmed up - I found them by using freezer spray, the soldering iron and a bit of tapping with a screwdriver.

Ging

[ppppenguin]

I've had TO18 transistors suffer an open circuit on occasion. From dim and distant memory they were mainly 2N706 ued on ex BBC video distribution amplifiers. I used to look after a lot of these and it was virtually a stock fault, after the electrolytics. There was often a bit of corrosion so I suspect it was damp storage in a previous life. Except that TO18 packages are meant to be watertight even if not fully hermetic.