Laser versus IR reflow soldering of eutectic tin-silver solder

Book · Sat Dec 31 00:00:00 EST 1994

OSTI ID:445301

Yang, W; Felton, L E; Messler, Jr, R W ^[1]

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1. Rensselaer Polytechnic Inst., Troy, NY (United States)

A computer-controlled 80W Nd:YAG laser operating in the continuous mode scanned beams of 10 to 60 watts at speeds from 2 to 60 mm/second over bare Cu pads on FR-4 fiberglass printed wire boards preprinted with a paste containing 96.5Sn-3.5Ag solder and RMA-SMQ51AC flux on which 132-pin quad flat-pack components were mounted. IR reflowed joints were made at 235 C with a 200 second soak. The high temperature, low heat input, and rapid cooling associated with laser soldering produced extremely fine eutectic rods of Ag{sub 3}Sn in essentially pure Sn, considerable equiaxed dendritic Cu{sub 6}Sn{sub 5} in the bulk solder, and thin Cu-Sn intermetallic layers at pad and wire interfaces. The lower temperature, higher heat input, and slower cooling rate associated with IR soldering produced coarser Ag{sub 3}Sn, far less Cu{sub 6}Sn{sub 5} dendrites in the bulk, and much thicker intermetallic layers at interfaces. Laser soldered joints were more than 50% harder than IR reflowed joints, suggesting higher static, creep and fatigue strength as well. Aging at 40 to 190 C for times up to 300 days reduced process-induced differences in structure and properties and revealed voids and cracks which led to the failure of solder joints.

• OSTI ID: 445301
• Report Number(s): CONF-940367-; ISBN 0-87171-441-8; TRN: IM9713%%37
• Resource Relation: Conference: advanced joining technologies for new materials II conference, Cocoa Beach, FL (United States), 2-4 Mar 1994; Other Information: PBD: 1994; Related Information: Is Part Of Advanced joining technologies for new materials 2: Proceedings; PB: 298 p.
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
42 ENGINEERING NOT INCLUDED IN OTHER CATEGORIES
SOLDERING
ELECTRONIC EQUIPMENT
EVALUATION
LIQUID METALS
TIN ALLOYS
SILVER ALLOYS
NEODYMIUM LASERS
INFRARED RADIATION
COMPUTERIZED CONTROL SYSTEMS
MICROSTRUCTURE
OPTICAL MICROSCOPY
SCANNING ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY
PHASE DIAGRAMS
INTERMETALLIC COMPOUNDS
MICROHARDNESS
AGING
EXPERIMENTAL DATA