Lasers and Residue

[junt0033]

Right now my company is trying to build a machine where we coil magnetic wire, wire strip the end leads, and solder these end leads of the coil to a flex circuit. Excimer lasers are used for wire stripping, but they are so expensive. We were thinking of using a TEA CO2 laser, but that leaves a residue that must be cleaned before soldering. We were thinking Plasma to clean the residue, but does anyone have any suggestions for a cheap clean process to wire strip, as well as a cheap clean process to solder? The wire is 41 AWG "polyurethane overcoated with polyamide and self bonding overcoat" (NEMA MW29-C) Whole assembly time for coil soldered to flex circuit I'm looking at 1 about every four minutes, so about 20 in an hour.
Need help
<p>[ August 17, 2005: Message edited by: junt0033 ]</p>

[jwax]

You left out the part about the insulation material. Is it just shellac as on magnet wire?
Also, are you doing a few of these, or is the machine going to do a hundred per minute? What size wire? 18 AWG may be a different process than 36 AWG. Details please, and welcome to the forum!

[junt0033]

<p>[ August 17, 2005: Message edited by: junt0033 ]</p>

[Engineer1138]

Eden Prairie? Dude, you're right down the road <p>I assume you've already considered a mechanical stripper. Why wouldn't that work?<p>If it's because of the number of moving parts in a mechanical stripper, perhaps the wire ends could be heated to high temp in a small "oven" with vacuum exhaust to remove the residue that's burned off

[junt0033]

we can't use a mechanical stripper due to the material of insulation. There has to be minimal damage, if any, to the wire which cannot be achieved with a mechanical stripper.

[jwax]

Mechanical strippers do not have to nic the wire!
Set up correctly, it will do fine without touching the wire.

[rshayes]

On very fine wire, it is common to use heat strippable insulation. Number 41 would be almost impossible to strip mechanically, since it is so small and fragile.<p>Try inserting the wire into molton solder on the tip of a soldering iron. Heat strippable insulation will burn off in a couple of seconds and the wire will come out tinned. Wait 4 or 5 seconds, and the wire will dissolve in the solder.<p>Some of the heat resistant insulations, such as formvar, can be stripped using special chemical solutions. General Cement used to supply chemical strippers for enamel and formvar. When the wire is dipped in the solution, the insulation softens and can be removed by wiping with soft tissue paper. Be careful with the solution, it is quite caustic.<p>[ August 22, 2005: Message edited by: stephen ]</p>

[jwax]

Until junt0033 returns to detail his project, all we can do is to guess what may work and what may not.

[Chris Smith]

"The wire is 41 AWG "polyurethane overcoated with polyamide and self bonding overcoat" (NEMA MW29-C) "<p>The most preferred method aside from the laser and vacuum method which requires OSHA to be heavely involved, is the heat stripper and acid bath. <p>If your not willing to invest in expensive equipment, the heat stripper will cut through the poly and Teflon, and the acid bath will insure the oxidization and residue is removed. <p>The acid is not totally environmentally unfriendly so it should be the path of least resistance.

[jwax]

Sorry about that. I missed the edit.
What Chris said!

[rshayes]

"polyurethane overcoated with polyamide and self bonding overcoat"<p>This is a two layer insulation system. Belden calls it "Beldsol". Other manufacturers probably have other names.<p>It is a heat strippable insulation designed to be removed with molton solder. When the wire is immersed in molton solder, the insulation burns off and rises to the surface of the solder. The wire comes out tinned.<p>There is usually a ring of carbon around the wire where it entered the solder. You can either leave it there or take it off with your fingers.<p>You don't need an acid bath, the tinning protects against corrosion.<p>Don't leave fine wire such as #41 in the molton solder for more than a few seconds. Copper will dissolve in molton solder and the wire will disappear.

[junt0033]

The reason I'm looking for a clean process for wire stripping is
a) residue presents yield for soldering
b) mechanical strippers on 41 AWG wire will, if not break, leave scratches on the wire itself. Or, if its thermal removal, will burn the insulation leaving, if not residue, a charred surface. Neither cases are acceptable for product approval.
We found a cheaper Excimer laser, and are now looking for clean soldering applications. Any suggestions such as selective reflow soldering? We want a non-liquid flux application since we are trying to stay away from chemicals. That has brought up the question on solder paste. We were thinking controlled atmosphere soldering, but we don't know a lot about it. We have also been looking into diode lasers for soldering purposes. We need to settle on a soldering system, and I don't necessarily know what type of soldering best fits my application.

[Chris Smith]

The Acid bath or Rosin bath should do the trick.<p> There are many different types out there.<p>The Residue[s] can build up and get in the way, so it is the perfered method and its simple. <p>They use a moving bath which circulates the cleaning agent through a filter to float away any build up and they raise the temperature of the agent so as to be more efficient.<p>The HOT wire strippers don’t nick the wire and they remove the bulk of the material away from the job which is always a biggie. There is nothing worse than a pile of melted dirty plastic in the soup. <p> The bath does the rest.<p>[ August 22, 2005: Message edited by: Chris Smith ]</p>

[junt0033]

I guess I wasn't clear on the point of us trying to stay away from chemicals. We are making a machine that winds a coil of magnetic wire, then wire strips the leads of the coil, only to to solder the coil leads to a flex circuit. We are providing an automated process to company that has been doing this process manually until now. They have been using the chemical "dip" so to speak, and are interested in other forms of insulation removal. That's why we are focusing on lasers and so forth.

[ncstateboy81]

I don't know how much control you have over the laser but what about trying to avoid a residue issue by not burning all the way through the insulation. only most of the way so that you can pull it off with a clean line. A similar thing could also be done with a mechanical stripper.<p>-------------------------------------------<p>I need a newbie disclaimer