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July 2004

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Subject:
From:
Daan Terstegge <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Daan Terstegge <[log in to unmask]>
Date:
Fri, 30 Jul 2004 09:18:34 +0200
Content-Type:
text/plain
Parts/Attachments:
text/plain (132 lines)
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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