Richard,
The 1/2 of the lead thickness spec is for class 2. Kevin's original post
requested info on class 3. Class 3 is solder thickness plus lead thickness.
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)594-0602 cell
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, March 07, 2006 8:45 AM
To: [log in to unmask]
Subject: Re: [TN] Heel Overhang
In order to meet the IPC-610 spec and the J-STD-001 spec for heel solder
fillet, the heel fillet must extend up the back side of the lead greater
than or equal to 1/2 of the lead thickness. If the heel is off of the pad
such that you do not get a heel fillet that meets this spec, it is too far
off and is a reject condition. The heel fillet is the most important part of
the solder joint, as it is the portion of the gullwing lead that is forming
an intermetallic compound with the finished portion of the lead. The side
fillet and the toe fillet form an IMF with only the exposed copper on the
cutaway portion of the lead. While having a toe and side fillet is good, the
heel fillet is of primary importance.
Without a heel fillet, the toe and side fillet presence is irrelevant, the
heel fillet must be present.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mary Jane Chism
Sent: Monday, March 06, 2006 12:00 PM
To: [log in to unmask]
Subject: Re: [TN] Heel Overhang
Kevin,
This is one of those "cumulative" conditions where in order for you to
evaluate "heel overhang", you would need to evaluate "Side Joint Length"
and "Minimum Fillet Height".
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Monday, March 06, 2006 11:29 AM
To: [log in to unmask]
Subject: [TN] Heel Overhang
Hello again.
Question on IPC-610 (class 3) criteria. For SMT solder joints, there appear
to be criteria set for TOE overhang, but not HEEL overhang. Is this an
oversite or a purposeful omission? Is there a limit on how much the heel of
an "L" shaped SMT lead can be off the pad lengthwise? The obvious and
defined limit is "does not violate minimum electrical clearance", but does
anyone else have info on this criteria?
Thanks again,
Kevin Glidden
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