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Toe Fillet Requirements on Gull Wing Components
Is a toe fillet required on gull wing components?
If it is not a requirement why is that so? We have some gull wing components that have no toe fillet, but all the other
requirements for the solder connection are met.
Per IPC-610, section 8.3.5 Flat Gull Wing Leads and section 8.3.6 Round or Flattened (coined) Gull Wing
Leads, there is no requirement for toe fillets. The only requirement is that if the lead overhangs the pad or
land area it does not violate the minimum electrical spacing requirements of the product.
The reasoning for not having a requirement for toe solder fillets is that the method of manufacturing for the
gull wing lead frames creates a condition on the end of the lead which may or may not be solderable.
Therefore we did not create a criteria for a solder fillet at the end of the leads, if it happens it is ok and if it
does not happen that is still acceptable.
The strength of the solder joint for gull wing components is in the heel fillet of the component and the length
of the component lead, so the solder joint at the toe of the component does not add anything to the strength
and reliability of the solder joint.
If all the other requirements are met except the toe fillet is missing as mentioned the condition is acceptable.
I hope this answers your question.
Vice President, Technical Director
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification
programs and provides customers with expert consultation in electronics manufacturing,
including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the
Assembly/Joining Process Committee.
Per J-STD-001, there is no requirement:
There is no reference to a minimum toe fillet height (Class 1, 2, and 3)
Toe overhang is permitted where it does not violate electrical clearances (Class 1, 2 and 3), in which
case by definition there is no toe fillet.
While this may seem odd, we need to realize that the toe of a gull-wing lead is under little or no mechanical
stress, because the component is attached at the heel end. In practice, nearly all failures of gull-wing joints
begin at the heel and propagate toward the toe. In addition, the fact that most gull-wing leads are formed and
cut after plating leaves the toe relatively unprotected from oxidation, and so getting a toe fillet may be
Fritz's career in electronics manufacturing has included diverse engineering roles including
PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering,
and electronics materials development and marketing. Fritz's educational background is in
mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques
have been an area of independent study. Fritz has published over a dozen papers at various industry
The NASA requirement is the width of the end solder joint (toe) must be greater than 75% of the lead width.
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development
group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly,
Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free
Visual Inspection and Lead Free Array Rework.
There is a requirement to have the pad extend past the toe of the lead... however, the solder presence cannot
be left to a toe fillet only. The design of the pads, coupled with the dynamics of the reflow will pull the
solder from heel to toe and vice/versa.
For this reason, the toe fill maximum requirement is often noted, but the minimum, due to control is not
defined as a defect.
Capital Equipment Operations Manager
Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and
Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing
from Purdue University, along with 20+ years of Electronic manufacturing and Equipment
Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating
equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.
Structurally the most significant elements of a gull-wing solder joint are the solder between the pad and the
bottom of the gull wing lead and the solder at the heel of the lead (heel fillet). Toe fillet can't be counted on
nor does it add any appreciable strength. Many gull-wing devices are sheared from their lead-frames after
lead-frame plating. This results in exposed basis material at the point of plating buss shearing.
So if the basis is unsolderable or tough to solder, as most are, it may not wet during the soldering process. A
good example of this would be a copper alloy lead-frame. Copper (sans OSP-coating) is notably difficult to
flux with typical No-Clean flux formulations. Plating is added to such lead-frames to allow reasonable
solderability during SMT processing.
Alloy 42 (Kovar) is another lead-frame alloy this is not solderable without the addition of a plating.
Therefore, there can be no expectation for toe fillet formation during soldering. Bottom Termination
components (BTCs) are another class of component with sheared lead and no reasonable prospect for toe
fillet formation. Lastly, recall that IPC 610 allows for some gull wing toe overhang beyond the PWB's
Certainly on an overhanging lead one could not expect to have a toe fillet. Concentrate on getting the rest of
the solder joint right, especially an in-spec (per -610) heel fillet.
A thirty year veteran of electronics assembly with major OEMs including Digital Equipment
Corp., Compaq and Hewlett-Packard. President of Colab Engineering, LLC; a consulting
agency specializing in electronics manufacturing, root-cause analysis and manufacturing
improvement. Holder of six U.S. process patents. Authored several sections and chapters on circuit assembly
for industry handbooks. Wrote a treatise on laser soldering for Laser Institute of America's LIA Handbook of
Laser Materials Processing. Diverse background includes significant stints and contributions in
electrochemistry, photovoltaics, silicon crystal growth and laser processing prior to entering the world of
PCAs. Member of SMTA. Member of the Technical Journal Committee of the Surface Mount Technology