Wire Wrapping IC Leads? - Page 1
Forum section: electronics / projects

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 21, 2014, 06:53:57 pm
content: I know, who would be so anal? Me apparently.I have a sensor that happens to be extremely sensitive to heat. I'm looking at other ways to attach it to a circuit. I've thought about a socket, zif or otherwise, and this may be the way I go. However, the idea of wire wrapping the IC leads on the sensor also appeared in my head.Does anyone have any experience with this? I realize the typical rectangular / flat IC lead is not a wire wrap post... but, how far off is it?

author: SeanB
author_rank: Super Contributor
timestamp: April 21, 2014, 07:19:01 pm
content: They do wire wrap, but you have to strip the wire, and use a modified wrap ( 2 turns of insulation around the lead) but the connection will not be reliable, as you are lacking the sharp edges in the socket leads. You can do it, but with time, temperature cycles and exposure to air it will corrode and ultimately it might go intermittent or noisy. i did do that, but soldered the wire afterwards.Coincidentally this evening I was looking at a wire wrap pen in a box, still has the Vero insulated wire spool in it, with the 22SWG wire ( I think) insulated wire in it.

author: David Hess
author_rank: Super Contributor
timestamp: April 21, 2014, 07:25:51 pm
content: Quote from: CaptnYellowShirt on April 21, 2014, 06:53:57 pmHow far off is it? A lot.The sharp edges if the square posts used in wire wrap construction allow the high pressure between the wire and post edges to fuse the metal together creating a hermetic joint. You can feel "cogging" from breaking the spots where the metals are fused together when unwrapping a joint.If you wrap the wire around a round post or the round lead of a part, corrosion between the wire and the lead tends to cause problems later. Soldering a wire wrapped joint is one way to avoid that but then it is a soldered joint and not a wire wrap joint.Good crimped joints work the same way to make them reliable. The crimping force should be high enough to fuse the metal creating a hermetic joint.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 21, 2014, 08:13:22 pm
content: I agree, it doesn't sound like wire wrapping would be a reliable solution.What about spring / screw terminals or rising cage clamps?

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: April 21, 2014, 08:17:26 pm
content: Any chance of a picky of the device so we can probe our minds for past connectors/ideas that might help

author: edavid
author_rank: Super Contributor
timestamp: April 21, 2014, 08:31:25 pm
content: Wire wrapping works temporarily - is that good enough?How about conductive epoxy?

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 21, 2014, 08:54:51 pm
content: Quote from: David Hess on April 21, 2014, 07:25:51 pmI'm familiar with IDC style connectors. A 3M app note on the subject shows the microscopic cross section of good and bad IDC crimps. As I remember, you can't see where the wire ends and the fork starts with most of the good ones them. Bad ones have a clear line or even voids between the wire and fork.I thought about crimping. Basically wire wrapping the terminal and then pressing the wraps in a arbor press.... but again unknown territory.Does anyone have information on how much pressure it takes to form a welded bond?

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 21, 2014, 08:56:17 pm
content: Quote from: Mr Smiley on April 21, 2014, 08:17:26 pmOh its super boring. Just a temperate sensing diode in a TO-92 case.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: April 21, 2014, 09:46:58 pm
content: As I recall the metal in a square wirewrap post is harder than that of an IC pin and standard wirewrap wire itself. Hence the ability to make a good connection provided that the environment was not subject to too much vibration.

author: David Hess
author_rank: Super Contributor
timestamp: April 21, 2014, 10:24:40 pm
content: A crimp connection or resistance welding would work well but if it is just a TO-92 packaged temperature sensor, what is wrong with soldering?With TO-92 and other small parts like resistors and capacitors, I have had good results using collet socket pins intended for IC pins. They make transistor sockets using them but just the pins themselves can be had cheaper but cutting up a SIP header or socket.

author: georges80
author_rank: Frequent Contributor
timestamp: April 21, 2014, 11:02:43 pm
content: Quote from: CaptnYellowShirt on April 21, 2014, 08:56:17 pmSo you have a device that in production would be soldered and you're worried about hand soldering it??? Seems a little paranoid... A TO-92 with leads? If you are really scared, then why not clip on a pair of tweezers etc while soldering each lead?cheers,george.

author: dfnr2
author_rank: Regular Contributor
timestamp: April 21, 2014, 11:03:16 pm
content: As mentioned above, a socket will work.However, the device is likely meant to be soldered. How are you trying to solder it? Wave soldering should be fine for most temp sensitive parts. Hand soldering should be fine, too, if you use good technique, and a decent soldering iron such as a metcal that can heat up the joint quickly. Placing a heat-sink clip on the lead close to the body can help dissipate head as well. If done right, the part shouldn't become more than warm to the touch, if that.What does the datasheet say?

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: April 21, 2014, 11:17:24 pm
content: Quote from: CaptnYellowShirt on April 21, 2014, 08:56:17 pmHow about a simple to-92 socket, at one time they were always used on pcb's. Don't see them much anymore .

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 21, 2014, 11:24:02 pm
content: Quote from: CaptnYellowShirt on April 21, 2014, 06:53:57 pmI'm just curious about the wire wrapping idea.Also, I did a little poking around on the web today about the cold weld pressure. One source said 8-10 times the material's yield strength.

author: edavid
author_rank: Super Contributor
timestamp: April 21, 2014, 11:26:24 pm
content: Quote from: CaptnYellowShirt on April 21, 2014, 08:56:17 pmWhat makes you say it's "extremely sensitive to heat"?

author: SL4P
author_rank: Super Contributor
timestamp: April 22, 2014, 01:04:30 am
content: I've wire-wrapped DIP chips before - dead-bug style - to save space, but as mentioned the wraps are not reliable in themselves - I trimmed the legs after, and touched them with solder to make a tiny, neat joint.It Worked well.The soldering limits of your component should be published somewhere.