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October 2012

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Subject:
From:
Phil Nutting <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Phil Nutting <[log in to unmask]>
Date:
Wed, 24 Oct 2012 16:45:27 -0400
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Richard,

I don't have any data to support or refute this.  The idea of soldering the wire BEFORE crimping goes along with the notion of the leaded solder "relaxing".  If the soldering is done AFTER crimping I don't think there will be solder relaxing as you had a good mechanical crimp before you unnecessarily added the solder.  If someone says to me they are worried about the solder melting I remind them that for the solder to melt it will require a very high temperature and it is a safe bet they have a bigger problem to worry about.

Phil

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]] 
Sent: Wednesday, October 24, 2012 3:28 PM
To: TechNet E-Mail Forum; Phil Nutting
Subject: RE: Crimping to AWG 8 solid magnet wire

Hi, Phil
I understand and totally agree with you and Steve, soldering stranded wire and then crimping is a bad idea.
The original reason was that the leaded solder would eventually relax and cause the crimp to fail.
However, is that still true with lead-free solder?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Wednesday, October 24, 2012 10:35 AM
To: [log in to unmask]
Subject: Re: [TN] Crimping to AWG 8 solid magnet wire

Gerald, et. al.,

Maybe this is a case of "if some is good, more has to be better".  Presumable the manufacturer has tested their terminal successfully at 60 psi, but did the end user not use the same gauge and type wire as the manufacturer tested.  Maybe someone assumed that more pressure would make a better joint and the idea stuck... "we have always done it that way".  Solid and stranded of the same gauge will actually have different wire diameters.

Some folks will assume that by soldering they make a better connection.  Not the case.

Some folks will say that they have to handle a lot of current so it needs to be soldered.  But the wire/lug combination can only handle the amount of current it is rated for without potential for failure.

The only place we use solder with crimps is when terminating Litz wire.  Litz is a whole bunch of fine enamel coated wires that each strand must be stripped to make a connection.  Chemical stripping and solder pot immersion are the only possible solutions.  Solder pot stripping is the most environmentally and manufacturing friendly.

Years ago we crimped and then soldered our terminals.  Bad practice!  I have converted our staff to agreeing that crimp and solder is incorrect.  The theory is that if the wire/lug combination has been properly sized and properly crimped that it will make a gas tight mechanical weld.  Adding solder does two possible detrimental things, flux wicked up the wire (not an issue for solid wire) and it makes the wire more susceptible to breakage due to wire fatigue (not an issue for solid wire).  Several years ago this discussion came up and I had Steve Gregory post a document that I had gotten from Amp that clearly stated that soldering was bad practice and it outlined exactly what I have listed above.

Just my opinion though.

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerald Bogert
Sent: Wednesday, October 24, 2012 10:26 AM
To: [log in to unmask]
Subject: [TN] Crimping to AWG 8 solid magnet wire

October 24, 2012



IPC/WHMA-A-620 includes the following requirements pertaining to crimping to solid wire.



a.     Crimping to solid wire is not allowed except for connector center
contact.

b.     Crimp tool cycle must be completed.



We have an OEM who crimps a solid AWG # 8 gage magnet wire (stripped to remove insulation) to a standard AN-8 (T&B) NAVY type terminal lug using a manual hydraulic crimp tool that has adjustable pressure settings.  If the crimp is performed at 90 PSI, one gets a complete tool cycle which leaves a deep crimp impression on the top surface of the lug and the # 8 impression on the reverse side of the lug.  One can see a bell-mouth at both ends of the lug.  If a 60 PSI setting is used, the crimp forms and one can see two small crimp impressions on the top of the lug but nothing on the back side of the lug.  Both settings result in the lug barrel forming around the OD of the stripped magnet wire.  The OEM uses the 60 PSI setting because of the concern of over crimping at the 90 PSI setting resulting in possible damage to the wire.  At one time the lugs were brazed rather than crimped but this process caused some lugs to crack so they changed from braze to crimp.



The contract drawing also mandates that the lugs be soldered after crimping and that the solder must flow to fill any voids inside the lug barrel.



Based on the above, I have the following questions that I would appreciate a response to:



1.     What is the technical basis for not allowing crimp to solid wire
for any solid wire other than for connectors and why would we not have the same concern for connector crimp?

2.     Would one expect solder to flow into the ID of the lug with the
60 or 90 PSI settings?

3.     Assuming the 60 psi crimp is pull tested and passed, is this a
technically acceptable crimp?  If not, why not?



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