Laser versus IR reflow soldering of eutectic tin-silver solder
- 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
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
42 ENGINEERING
AGING
COMPUTERIZED CONTROL SYSTEMS
ELECTRONIC EQUIPMENT
EVALUATION
EXPERIMENTAL DATA
INFRARED RADIATION
INTERMETALLIC COMPOUNDS
LIQUID METALS
MICROHARDNESS
MICROSTRUCTURE
NEODYMIUM LASERS
OPTICAL MICROSCOPY
PHASE DIAGRAMS
SCANNING ELECTRON MICROSCOPY
SILVER ALLOYS
SOLDERING
TIN ALLOYS
X-RAY SPECTROSCOPY