Lead-free lead oxide? - Page 1
Forum section: electronics / general

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 12:05:13 pm
content: Spent a few hours this evening loading PCB's for my analog computer project. I have stock of KSA1381/KSC3503 TO-126 transistors that I bought a couple of years ago. The leads have gone white with what I guess is an oxide layer. I have hundreds of these TO-126's to load and this is making the job more tedious than it should be. The hole spacing is the standard 100 thou, but that seems a fraction tight. When the transistor is pushed home the outer leads of the package are splayed slightly and the action of the inside edge of the leads rubbing against the PCB hole edges causes a layer of the oxide to be scraped off, often resulting in a neat little conductive (?) whisker bridging adjacent pads. After inserting each transistor I have to pull it out again and scrape the leads clean.Is this annoyance the product of lead-free leads? How would you deal with this in automated production?

author: SeanB
author_rank: Super Contributor
timestamp: July 13, 2014, 12:27:25 pm
content: Production would toss them and buy new, or would have kept them in a hermetic package along with a desiccant pack and a non oxygen permeable lining.You can simply take each device and get a block of floral foam and push the leads into it and out before insertion, this gentle abrasion will clean the leads bright again. You will just have to trim the top layer of the foam block every so often to get a clean surface not full of holes.

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 12:51:03 pm
content: Quote from: SeanB on July 13, 2014, 12:27:25 pmThese come straight from the manufacturer in non-air-tight tubes. You couldn't have them sitting on the shelf for very long without going like this.

author: rob77
author_rank: Super Contributor
timestamp: July 13, 2014, 01:06:41 pm
content: proxxon/dremel with polishing disc - approx 2 seconds per transistor

author: SeanB
author_rank: Super Contributor
timestamp: July 13, 2014, 01:30:13 pm
content: True, but they probably have most of them that are shipped used within 60 days, and stored in an area with controlled temperature and low humidity. Likely the manufacturer keeps them in a CA store in any case just to have an acceptable shelf life for the batch.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 13, 2014, 02:53:10 pm
content: RTFDS -- the lead spacing is 2.28 mm.I'm impressed your PCB is sharp enough to actually scrape the leads. Probably not a good sign though.If you can't change the footprint now, form the leads. Make a jig, or do it by hand. Each and every time...Also, the leads are 0.75 x 0.5 mm, which need holes over 0.9 mm. 1 mm (40 mil) should be sufficient.Tim

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 11:35:04 pm
content: Holes are 1mm. The white coating requires little effort to scrape off.I am still blown away at how badly and quickly these lead-free leads develop this white coating.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 13, 2014, 11:37:25 pm
content: What's pictured just looks like matte tin. Can you get a better picture showing the whiteness?Tim

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 11:49:44 pm
content: Not really. That photo was the clearest out of about 10 made with my crappy camera. Anyway I have a box of fine steel wool handy and that fixes the problem easilly enough.

author: ConnorGames
author_rank: Regular Contributor
timestamp: July 15, 2014, 03:04:42 am
content: Be REALLY carefull with the steel wool -- that stuff gets little conductive metal fibers EVERYWHERE!

author: AlfBaz
author_rank: Super Contributor
timestamp: July 15, 2014, 03:26:56 am
content: Quote from: GK on July 13, 2014, 11:49:44 pmLOLTrying to focus on the subject is the mistake. Try focusing on anything but the subject and Murphy will sort you out

author: John Coloccia
author_rank: Super Contributor
timestamp: July 16, 2014, 11:02:52 am
content: 2 seconds with an eraser should take that right off. Just do the whole batch at the same time.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 17, 2014, 02:39:12 pm
content: Date stamp looks like 423, if bought a couple of years ago then that must be 2004 at least, 1974 at worst?

author: thm_w
author_rank: Super Contributor
timestamp: July 17, 2014, 11:17:26 pm
content: Quote from: woodchips on July 17, 2014, 02:39:12 pmhttp://www.fairchildsemi.com/pf/KS/KSA1381.htmlhttp://www.fairchildsemi.com/support/packaging/topmark/dateCode3/J = 2008, lead free. So much for a "couple" of years :p

author: rob77
author_rank: Super Contributor
timestamp: July 18, 2014, 12:15:19 am
content: Quote from: thm_w on July 17, 2014, 11:17:26 pm6 is still 3 couples

author: Monkeh
author_rank: Super Contributor
timestamp: July 18, 2014, 12:33:12 am
content: Quote from: rob77 on July 18, 2014, 12:15:19 amJust enough for a good time!