Hi All,
We looked at this during creation of the current requirements content and tried to arrive at a point where the lead should be considered toe down.
A couple of points were discussed at length.
We certainly don't want to cause inspectors to attempt to measure angles of lead toe down to determine acceptance.
Reliability data was not available to support a specific value of toe down for reference in the standard.
The result was: Those components that normally have a toe down configuration have different requirements from those that do not, but the presence of a heel fillet is still necessary for connection performance reliability. No specific angle was available or referenced at the time. This leaves it up to the user of the document to determine the condition of the actual component and to apply the correct criteria as appropriate.
Should there be supporting data to apply a value to this condition, the committee would be most interested in considering the inclusion in Revision D, now under construction.
The 001 and 610 committees meet next week in Huntsville.
Best regards,
Mel
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Guy Ramsey
Sent: Friday, July 30, 2004 3:32 PM
To: [log in to unmask]
Subject: Re: [TN] Toe-down configuration for gull wing leads
There are a couple of ways. In the back of the IPC-A-610 there is a standard
improvement form. You can FAX it to the IPC. You can also contact Jack
Crawford ( [log in to unmask] ) with your proposed change and rational. It
is very helpful if you identify the clause you want changed, propose a new
requirement, and explain why you think the change is an improvement.
I see your point. I guess you might get parts with insufficient bend,
causing a gap underneath the component lead. Solder results would be poor
because of insufficient solder volume. I don't know how the committee would
reach on consensus for that case. I think they would lean toward rejecting
the components.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Daan Terstegge
> Sent: Friday, July 30, 2004 3:19 AM
> To: [log in to unmask]
> Subject: Re: [TN] Toe-down configuration for gull wing leads
>
> Hi Guy,
>
> Also larger packages sometimes have their leads bent in such
> a way that it makes a really huge difference whether the
> fillet should extend to the mid-point of the lead bend or
> not, and even with thick stencils and long solderpads it is
> not always possible.
> I don't think there's a mistake, but the exact definition of
> "toe-down configuration" should be included the spec,
> otherwise you can call everything "toe-down" even when the
> angle with the pad is 0.0001°. But from the A-610 and
> J-STD-001 it seems that toe-down is not the rule but the
> exception to the rule.
> So how can I contact the comittee ?
>
> Daan Terstegge
>
> >>> [log in to unmask] 07/29/04 11:41pm >>>
> The standards Both J-STD-001 and IPC-A-610 (C not B) say that
> the solder must extend to the mid-point of the outside of the
> lead bend. It is possible to achieve this condition if the
> land pattern and solder stencil are properly designed. There
> is a pretty large process window, as this lead configuration
> is generally associated with low lead packages and the
> maximum solder condition allows solder to extend under and
> touch the component body.
>
> If you think there is a mistake in the standard, now is the
> time to act. The committees are well along in the development
> of revision D.
>
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Charles Caswell
> > Sent: Thursday, July 29, 2004 5:24 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Toe-down configuration for gull wing leads
> >
> > J-STD rev.B in front of me. You are correct, it does say to the
> > midpoint of the lower bend radius. My opinion is this is a mistake.
> >
> > -----Original Message-----
> > From: Daan Terstegge [mailto:[log in to unmask]]
> > Sent: Thursday, July 29, 2004 3:03 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Toe-down configuration for gull wing leads
> >
> >
> > Hi Charles,
> >
> > This kind of problem is exactly why I ask the question.
> > Normal requirement is indeed having an amount of solder in
> > the heel which is equal to the leadthickness (for class 3),
> > but for toe-down the solder must extend to the midpoint of
> > the lower bend, which is -as you say- not always possible.
> > Therefore it is important to know if one has to look at the
> > whole lead, the last millimeter of the lead, the last 10th of
> > a millimeter or whatever. When
> > (only) the last few mils of the tip of the lead are parallel
> > to the pad, would that mean it is no longer a "toe-down
> > configuration" ?
> > Accepting your definition, my question would be: which part
> > of the lead is exactly defined as the "foot of the lead" ?
> >
> > Daan
> >
> > ----- Original Message -----
> > From: "Charles Caswell" <[log in to unmask]>
> > To: <[log in to unmask]>; <[log in to unmask]>
> > Sent: Thursday, July 29, 2004 9:15 PM
> > Subject: RE: [TN] Toe-down configuration for gull wing leads
> >
> >
> > If the foot of the lead is not parallel to the pad it is toe
> > down. The solder requirement would be one lead thickness, On
> > toe down this does not usually come up to the heel bend
> > radius.I have trouble with this every time.
> > Inspectors want to see the fillet above the midpoint of the
> > heel, but with toe down it is not always possible or practical.
> >
> > -----Original Message-----
> > From: Daan Terstegge [mailto:[log in to unmask]]
> > Sent: Thursday, July 29, 2004 12:12 PM
> > To: [log in to unmask]
> > Subject: [TN] Toe-down configuration for gull wing leads
> >
> >
> > Hi Technet,
> >
> > The IPC-A-610 (and related specs) mentions special
> > requierments for solder joint heel fillets when the leads
> > have a "toe down configuration". I was wondering if a
> > definition exists of what exactly a toe down configuration
> > is. If the last portion of the tip of the lead is not 100%
> > parallel with the solderpad but has a small angle, does that
> > mean it's a toe down configuration ?
> > You help is appreciated as always,
> >
> > Daan Terstegge
> > http://www.smtinfo.net
> >
>
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