Hi Steve:
The heels hanging on the breeze is a "Toe Down"
lead prep condition, due to the die, used to prep the component, being
damaged by use or misuse. In that case, the fillet must reach half way
the thickness of the lead or to the top of the lead for class 2 and 3
respectively. There is a "Toe Up" condition as well.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: Monday, March 06, 2006 2:25 PM
To: [log in to unmask]
Subject: Re: [TN] Heel Overhang
Hi Kevin!
In reading my IPC-HDBK-001, at 6.4.1.8 it states:
SURFACE MOUNTED DEVICE LEAD HEEL CLEARANCE - The heel must not overhang
the land.
NOTE: The heel is defined as the point where the lead begins to curve at
the lead bend.
Then at 6.4.1.11 it states:
POSITIONING GULL-WIND LEADED DEVICES - It is preferred that leads be
seated in contact with the land for the full length of the foot.
This is just the handbook, not a spec.
That being said, I have built many boards that for instance a footprint
was laid-out for a socket (Programmable Device), and then the socketed
component was soldered directly to the PCB later on, with just the toes
and about 3/4 of the foot on the pads...the heels were hanging in the
breeze.
Not a good idea I know...
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Monday, March 06, 2006 10:29 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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