SURFACE MOUNT TECHNOLOGY (SMT)
SOLDER PASTE/SOLDER PREFORM APPLICATION
solder paste preform application
SOLDER PASTE/PREFORM APPLICATION

Solder paste is a mixture of solder alloy particles, flux and other materials for use in reflow soldering (oven, vapor phase or infrared) of surface mount technology (SMT) components.

Solder preforms are generally made from solder alloy wire or stamped from solder alloy sheet material, and formed into specific shapes (typically toroids, washers or donuts) for use in reflow soldering (oven, vapor phase or infrared) of Plated Through Hole (PTH) components and some Surface Mount Technology (SMT) components.
solder paste application solder preform application

ACCEPTABLE

SOLDER PASTE APPLICATION

The paste is applied in a uniform thickness, with proper alignment and placement. There is no bridging, bubbles, crusting, separation or smearing.

NASA-STD-8739.2 [8.2], [8.6]

ACCEPTABLE

SOLDER PREFORM APPLICATION

The preforms are applied with proper alignment and placement.

Best Workmanship Practice
bridging of lands bubbles in the paste

UNACCEPTABLE

BRIDGING

Bridging of lands is an indicator of improper screen alignment/paste application.

NASA-STD-8739.2 [8.7.4.f], [12.6.1.a.1]

UNACCEPTABLE

BUBBLES

Bubbles in the paste are typically caused by over-mixing and can affect solder joint formation.

NASA-STD-8739.2 [12.6.1.a.3]
NASA WORKMANSHIP STANDARDS
NASA logo Released:
06.27.2002 		Revision:
 		Revision Date:
Book:
7 		Section:
7.02 		Page:
1




SURFACE MOUNT TECHNOLOGY (SMT)
SOLDER PASTE/SOLDER PREFORM APPLICATION (cont.)
crusting of paste excess flux

UNACCEPTABLE

CRUSTING

Crusting of paste is an indicator of improper curing or use of expired material.

NASA-STD-8739.2 [6.12.2.d.6]

UNACCEPTABLE

EXCESS FLUX

Excess flux can degrade the formation of the solder fillet, leading to porous or rosin solder joints.

Best Workmanship Practice
incorrect coverage of solder paste incorrect placement of solder paste

UNACCEPTABLE

INCORRECT COVERAGE

Solder paste coverage, which exhibits properties less than those specified by engineering documentation, shall be rejected.

NASA-STD-8739.2 [12.6.1.a.4]

UNACCEPTABLE

INCORRECT PLACEMENT

Incorrect placement of solder paste/preforms is an indicator of an improper process parameter.

NASA-STD-8739.2 [12.6.1.a.5]
isolated deposit misalignment of solder paste

UNACCEPTABLE

ISOLATED DEPOSIT

Isolated deposition of solder paste is an indicator of a process control problem.

NASA-STD-8739.2 [12.6.1.a.2]

UNACCEPTABLE

MISALIGNMENT

Solder paste misalignment shall not be in excess of 25% of the spacing between lands.

NASA-STD-8739.2 [12.6.1.a.5]
NASA WORKMANSHIP STANDARDS
NASA logo Released:
06.27.2002 		Revision:
 		Revision Date:
Book:
7 		Section:
7.02 		Page:
2




SURFACE MOUNT TECHNOLOGY (SMT)
SOLDER PASTE/SOLDER PREFORM APPLICATION (cont.)
missing paste deposit paste separation

UNACCEPTABLE

MISSING DEPOSIT/PREFORM

Missing paste deposits or preforms are an indicator of an improper process.

NASA-STD-8739.2 [8.2]

UNACCEPTABLE

PASTE SEPARATION

Paste which exhibits separation shall be rejected.

Best Workmanship Practice
smearing

UNACCEPTABLE

SMEARING

Smearing that bridges conductors or lands is an indicator of an improper process or handling and shall be rejected.

NASA-STD-8739.2 [8.7.4.f], [12.6.1.a.6]










NASA WORKMANSHIP STANDARDS
NASA logo Released:
06.27.2002 		Revision:
 		Revision Date:
Book:
7 		Section:
7.02 		Page:
3





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