PREFERRED

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

NASA-STD-8739.2 [7.1], [12.8.1], [12.9.3.a]

PREFERRED

COPLANARITY

The lead's foot should be parallel to, and in full contact with, the termination pad.

NASA-STD-8739.2 [7.1]

ACCEPTABLE

COPLANARITY

The maximum acceptable variation in 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], [12.8.1.h]

UNACCEPTABLE

IMPROPER COPLANARITY

Excessive non-planarity may result in open or mechanically weak solder terminations, excessive part tilt, solder contact with the component body, or violate minimum electrical spacing requirements.

NASA-STD-8739.2 [12.8.2.a.10]

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 (C) 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 is less than 75% of the lead width.

Best Workmanship Practice

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

MANDATORY

HEEL FILLET

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

NASA-STD-8739.2 [12.9.3.a.1]

UNACCEPTABLE

MISSING HEEL FILLET

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

NASA-STD-8739.2 [12.9.3.a.1], [12.9.3.b.6]

ACCEPTABLE

HEEL FILLET HEIGHT (F)

The fillet height shall not exceed 50% of thelead height. The fillet may be convex, but shall exhibit a positive wetting angle, and the lead contour shall be visible.

NASA-STD-8739.2 [12.9.3]

UNACCEPTABLE

INSUFFICIENT HEEL FILLET HEIGHT

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

NASA-STD-8739.2 [12.9.3.b.3], [12.9.3.b.6]

PREFERRED

LATERAL/SIDE OVERHANG (A)

There should be no lateral/side overhang, the component lead should be cnetered on the land.

NASA-STD-8739.2 [12.6.2.a.5]

ACCEPTABLE

LATERAL/SIDE OVERHANG (A)

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

NASA-STD-8739.2 [12.6.2.a.5]

UNACCEPTABLE

IMPROPER LATERAL/SIDE OVERHANG

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

NASA-STD-8739.2 [12.6.2.a.5], [12.9.3.b.1]

ACCEPTABLE

MISSING TOE FILLET

A toe fillet is not required. However, the termination shall exhibit complete wettign and a positive wetting angle between the lead an termination pad.

Best Workmanship Practice

PREFERRED

SIDE JOINT FILLET (D)*

The side joint fillet shall be three times (3X) the lead width (W), ans shall exhibit a positive contour. (* See Nonwetting for exclusion.)

Best Workmanship Practice

UNACCEPTABLE

INSUFFICIENT SIDE JOINT FILLET (D)

The side joint fillet (D) shall be three times (3X) the lead width (W), and shall exhibit a postivie contour.

Best Workmanship Practice

PREFERRED

SOLDER THICKNESS (G)

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

Best Workmanship Practice

UNACCEPTABLE

EXCESS SOLDER

The solder fillet may be convex, but shall exhibit a positive wetting angle, the lead contour shall be visible, and the solder shall not contact the component body.

NASA-STD-8739.2 [12.8.1.c], [12.9.3.b.4]

UNACCEPTABLE

INCOMPLETE SOLDER FILLET

The solder fillet shall extend to the land edge.

NASA-STD-8739.2 [12.8.1.b]

UNACCEPTABLE

INSUFFICIENT SOLDER QUANTITY

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

NASA-STD-8739.2 [12.9.3.b.3]

ACCEPTABLE

TOE OVERHANG

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

NASA-STD-8739.2 [12.6.2.a.5]

UNACCEPTABLE

EXCESSIVE TOE OVERHANG

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

NASA-STD-8739.2 [12.6.2.a.5], [12.9.3.b.2]

UNACCEPTABLE

HEEL OVERHANG

Heel overhang is prohibited, as this condition routinely results in toe overhang (on the opposite side of the device), and may prevent the proper formation of a heel fillet.

Best Workmanship Practice