PREFERRED

The part is properly oriented to the land pattern, with each lead centered across the width of the land. Leads are planar, fillets are shiny and concave, and heel fillet is evident.

NASA-STD-8739.2 [8.7.4.h], [12.6.2], [12.8]

PREFERRED

COPLANARITY

The preferred planarity of the lead to the land pattern area is with the foot parallel and in full contact with the pad.

NASA-STD-8739.2 [7.1]

ACCEPTABLE

COPLANARITY

The maximum acceptable non-planarity between any portion of the lead foot and the pad shall not exceed 0.26 mm (0.010").

NASA-STD-8739.2 [7.1], [12.9.2.b.3]

UNACCEPTABLE

IMPROPER COPLANARITY

The maximum acceptable non-planarity between any portion of the lead foot and the pad shall not exceed 0.26 mm (0.010").

NASA-STD-8739.2 [12.9.2.b.3]

PREFERRED

END JOINT WIDTH (C)

The width of the end joint (C) should be greater than or equal to the lead width (W).

Best Workmanship Practice

ACCEPTABLE

END JOINT WIDTH (C)

The width of the end joint shall be greater than or equal to 75% of the lead width (W).

Best Workmanship Practice

UNACCEPTABLE

INSUFFICIENT END JOINT WIDTH (C)

The width of the end joint (C) is less than 75% of the lead width (W).

Best Workmanship Practice

MANDATORY

HEEL FILLET

A heel fillet is mandatory and the contour shall be positive.

NASA-STD-8739.2 [12.9.2.b.5]

UNACCEPTABLE

MISSING HEEL FILLET

A missing heel fillet is an indicator of improper process, and may impact the long-term reliability and integrity of the solder termination. A heel fillet is mandatory and the contour shall be positive.

NASA-STD-8739.2 [12.9.2.b.5]

PREFERRED

LATERAL/SIDE OVERHANG (A)

The target condition is no lateral/side overhang (A), with the component lead centered on the land.

NASA-STD-8739.2 [8.7.4.h], [12.6.2]

ACCEPTABLE

LATERAL/SIDE OVERHANG (A)

Lateral/side overhang shall not exceed 25% of the lead width (W), and shall not violate minimum electrical spacing requirements.

NASA-STD-8739.2 [8.7.4.h.l], [12.6.2.a.4]

UNACCEPTABLE

IMPROPER LATERAL/SIDE OVERHANG

Lateral/side overhang shall not exceed 25% of the lead width (W), and shall not violate minimum electrical spacing requirements.

NASA-STD-8739.2 [12.9.2.b.1]

ACCEPTABLE

MAXIMUM HEEL FILLET HEIGHT (E)

Solder may extend through the stress relief bend, but must not contact the lead seal. Solder shall exhibit a concave fillet and the lead contour shall be visible.

NASA-STD-8739.2 [12.8.1.b], [12.8.2.b.16]

UNACCEPTABLE

EXCESS SOLDER

The lead contour is not discernable; the solder extends through the stress-relief bends; and, the solder contacts the component body and seal.

NASA-STD-8739.2 [12.8.2.b.12], [12.8.2.b.16], [12.9.2.a.2]

ACCEPTABLE

MINIMUM HEEL FILLET HEIGHT (F)

The fillet height shall be equal to or greater than the minimum solder thickness (G), plus one (1) lead thickness (T).

Best Workmanship Practice

UNACCEPTABLE

INSUFFICIENT HEEL FILLET HEIGHT (F)

The heel fillet height is less than the minimum solder thinckness (G), plus one (1) lead thickness (T). This may result in a weakened solder termination.

Best Workmanship Practice

ACCEPTABLE

SIDE JOINT FILLET (D)

The side joint fillet (D) shall be present, equal to the lead width (W) plus the heel fillet, or equal to a minimum of 75% of lead length (L) plus the heel fillet, whichever is less, and exhibit complete wetting and a positive contour.

Best Workmanship Practice

UNACCEPTABLE

SIDE JOINT FILLET (D)

The side joint fillet shall be present, equal to the lead length (L) plus the heel fillet, and exhibit a positive contour.

NASA-STD-8739.2 [12.8.1.b]

PREFERRED

SOLDER THICKNESS (G)

The solder thickness shall be sufficient to form a properly wetted, concave fillet which extends over the complete periphery of the connection.

NASA-STD-8739.2 [12.8.1.b], [12.9.2.a]

ACCEPTABLE

MAXIMUM SOLDER

Solder quantity is at maximum, with the fillet extending up to the lead bend and completely covering the lead. The connection exhibits a well-wetted concave fillet on all sides, and the lead contour is discernable.

NASA-STD-8739.2 [12.8.1.b], [12.9.2.a]

ACCEPTABLE

MINIMUM SOLDER (B)

Solder quantity is minimum, but the connection is well wetted on all sides, with a concave fillet between the lead and the land. A heel fillet is evident and properly formed.

NASA-STD-8739.2 [12.8.1.b], [12.9.2.a]

UNACCEPTABLE

INSUFFICIENT SOLDER

The solder quantity shall be sufficient to form a properly wetted fillet.

NASA-STD-8739.2 [12.8.2.b.6]

ACCEPTABLE

NONWETTING
(SPECIAL EXCLUSION)

Leads not having wettable sides (edges) by design (such as leads stamped from pre-plated stock) are not required to exhibit side fillets.

Best Workmanship Practice

UNACCEPTABLE

IMPROPER WETTING

The solder fillet shall exhibit a positive wetting angle, wet all elements of the connection, and shall extend to the edge of the pad.

NASA-STD-8739.2 [12.9.2.a.1], [12.9.2.b.4]

ACCEPTABLE

TOE OVERHANG (B)

Toe overhang (B) shall not exceed 25% of the lead width (W), and shall not violate minimum electrical spacing (e) requirements.

NASA-STD-8739.2 [8.7.4.h.2], [12.6.2.a.5]

UNACCEPTABLE

EXCESSIVE TOE OVERHANG (B)

Toe overhang (B) shall not exceed 25% of the lead width (W), and shall not violate minimum electrical spacing (e) requirements.

NASA-STD-8739.2 [12.6.2.a.4], [12.9.2.b.2]

UNACCEPTABLE

HEEL OVERHANG

Heel overhang is prohibited.

Best Workmanship Practice