A long time ago, we once had a cutter for cropping leads after wave solder,
but it was peculiarly unreliable in its consistency. The blades would go
blunt very quickly and make a dreadful job of cutting leads cleanly. When
the lead is cut almost through, the weight of the lead and the pressure of
the cutter tended to break rather than cut the final part leaving rather a
rag or a smear. We gave up using the machine eventually and took to hand
cropping, but the shock of the 'snap' as the cutters through each lead
cannot have been very good for the joints.
The kindest way to treat the solder joints is to preform and trim the leads
so that they are soldered only once and require no cropping at all. We
found that many components habitually rode up in the solder wave to the
extent that minimum protrusion wasn't always achieved and rework had to be
performed. The test jig we had then couldn't handle clinched leads, though
that is the best way to go - preform, insert, clinch (half or full), trim,
solder.
Be careful cutting the leads of any components with a glass-to-metal seal -
they really don't like too much shock, so hand-cutting should be avoided.
Pete Duncan
"Pelchat,
Janice" To: [log in to unmask]
<JANICE.PELCHAT@ cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
BENCH.COM> Subject: Re: [TN] Lead protrusion
Sent by: TechNet
<[log in to unmask]
>
07/13/01 06:53
PM
Please respond
to "TechNet
E-Mail Forum.";
Please respond
to "Pelchat,
Janice"
Where I worked before, the wave solder machine had an inline cutter that
worked with the machine.
Solder, inline cut (Circular saw on its side basically), resolder, out the
other end. No manual cutting allowed.
Jan Pelchat
Benchmark Electronics
> -----Original Message-----
> From: Dorothy M. Lush [SMTP:[log in to unmask]]
> Sent: Thursday, July 12, 2001 7:32 PM
> To: [log in to unmask]
> Subject: Re: [TN] Lead protrusion
>
> Peter,
> Bill is right about the need to avoid trimming leads after solderwave.
The
> thicker the lead and/or cheaper the cutter the more likely there will be
a
> cracked solder joint. IPC class-2 says that this cracked solder joint
does
> not need to be remelted and class-3 says it does. Class-2 recommends
> 60-100
> mils lead length unless otherwise specified by the customer. If you are
> building to Class-2 and you don't want a possible lab or field failure
> because of a cracked solder joint then think and plan ahead to avoid
> having
> to trim. The thinking and planning includes the final assembly the PCA
> will
> be in. For instance, clearance for slot cards to slid in and out.
> Connector
> leads under a front panel even with an insulation strip can cut through
> the
> insulation eventually fail. I had a customer who wanted me to trim 70
mil
> plus diameter pins to 30 mils on the off the shelf power supply instead
of
> ordering the right length leads. They would have to be machined to do
that
> which can lead to other defects.
> Dorothy Lush
>
> > ----------
> > From: Kasprzak, Bill (sys) USX[SMTP:[log in to unmask]]
> > Reply To: TechNet E-Mail Forum.;Kasprzak, Bill (sys) USX
> > Sent: Thursday, July 12, 2001 12:58 PM
> > To: [log in to unmask]
> > Subject: Re: Lead protrusion
> >
> > Peter:
> >
> > Personally, I like .090", but typically I have to hold between .040 and
> > .060. In my mind, I think you would like to install parts with the
> correct
> > lead length prior to wavesoldering. Avoid having to trim after
soldering
> > is
> > always a good idea.
> >
> > Bill Kasprzak
> > Moog Inc., Electronic Assembly Engineering
> >
> >
> > > -----Original Message-----
> > > From: PL [SMTP:[log in to unmask]]
> > > Sent: Thursday, July 12, 2001 2:26 AM
> > > To: [log in to unmask]
> > > Subject: [TN] Lead protrusion
> > >
> > > Hello,
> > >
> > > Does anyone know what is the standard used for prepping
> > > the leads for through-hole boards?
> > >
> > > What are the critical parameters one should consider
> > > when determining the amount of trimming on the leads?
> > >
> > > Rgds,
> > > Peter
> > >
> > >
> > > _________________________________________________________
> > > Do You Yahoo!?
> > > Get your free @yahoo.com address at http://mail.yahoo.com
> > >
> > >
> >
>
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