Test data requirements for assessment of alternative Pb-free solder alloys
Table 1 (continued). Summary of test methods, parameters, controls, and reporting requirements for the assessment of new Pb-free solder alloys.
Test and method Test parameters Control Report
Design of Experiment (DOE) for Variables and test conditions: SAC305 Report:
miniport rework alloys and copper • Pot temperature (°C): 240 , 270, 300 (validated by a • Through hole fill results and example photos of visual
dissolution assessment thermocouple at the test setup) inspection to IPC-610 for J3
• Contact time (sec): 20, 40, 60, 80, 100 (measured • Cross-section images for pin 1, 56, 128, 129, 185, and 256
HP rework process characterization with a stopwatch and validated against the machine of J3
test method setting) • Copper dissolution measurements on cross-sectioned joint
Samples: Culebra PCAs from nominal wave process (see samples of J3 as compared to J2 (at pins above)
Wave and minipot rework solder wave DOE above), all components loaded EXCEPT J2, • IMC thickness measurements on cross-sectioned joint
alloys only which is taped to protect from soldering in wave, 60 new samples of J3 (at pins above)
alloy boards and 60 SAC305 boards
• Laminate defect evaluation and copper via cracking evaluation
Preconditioning: prior to wave, precondition PCBs with
for J3 (at pins above)
two nominal Pb-free reflow cycles
• Equipment and process parameters:
Rework component: J3 256 pin DIMM, remove and
a) Nozzle
replace the J3 connector during a single heat cycle within
b) Flow rate
the ‘contact time’ variable
c) Sample run order
Flux: Cookson OM338PT paste flux, applied immediately
d) Thermal profile
before preheat, also applied to new connector pins
Replicates: two replicates of the 15 conditions for each of
the following combinations:
• SAC305 wave and SAC305 rework
• new alloy wave and SAC305 rework
• new alloy wave and new alloy rework
• SAC305 wave and new alloy rework
Equipment: AirVAC PCBRM15 system with computer-
controlled time and pre-heater, board support fixtures, and
support fixtures that extend into the preheat area
Flow rate: characterized before the experiment with low
and high knob settings at a nominal temperature and
time (270°C, 60 sec), then fixed (this requires laminar
flow and constant pot [full] level, 1/4 inch from the lip of
the pot) Preheat time and temperature: Flux before
preheat. Board must reach a temperature between 120°C
and 130°C. Use instrumented, board-monitoring, board
temperature techniques (calibrate using an instrumented
assembly with thermocouples on both top and bottom
sides) for verification. Using an instrumented board placed
over the pot, monitor and record a profile for at least one
specific pin using three different thermal energies (profiles
at high temperature and time, low temperature and time,
and mediumtemperature and time). If possible, try to find
the coolest node.
TH fill measurement: Measure cross-sectioned joints
(or 5DX) on J3 as an actual measurement in millimeters
expressed as pin-wetted length
Copper dissolution measurement: Measure the
remaining copper of the TH pad and knee in cross-
sections on J3. J2 is the unpopulated sites for
determination of the ‘original’ thicknesses.
Material Properties
Property and test method Test parameters Control Report
Liquidus and solidus temperature As per test method SAC305 T
L
and T
S
in ºC, and graph of heat flow versus temperature.
DTA or DSC by ASTM E794-06
Electrical resistivity Test at 293ºK None Electrical resistivity (p) in µΩ-cm
ASTM B193-02
Thermal conductivity Measured or calculated from electrical resistivity test None Thermal conductivity (k) in W/(m-K)
at 293ºK
Young’s modulus, shear modulus, Sample must be a rectangular bar with a length to SnPb Measured E and G in GPa, and calculated Poisson’s ratio (v).
and Poisson’s ratio thickness ratio of 20:1 to 25:1 and a width to thickness
Ultrasonic stress wave propagation ratio of at least 5:1. Use equations (2) and (4) to determine Report geometry of test sample.
technique by ASTM 1875-00 the elastic modulus (E), equation (8) to determine the
shear modulus (G), and equation (15) to determine
Poisson’s ratio (v).
Stress-strain curve, 0.2% Test conditions: • Temperature (ºC): -25 (optional), 25, SAC305 Plot the engineering stress vs. engineering strain (to failure),
yield strength, ultimate tensile 75, 125, 160 • Rate: 3 mm/min (resulting in strain rate of measured by conventional tensile testing for both alloys at each
strength,and elongation 10-3 s -1 ) temperature. Average the three samples at each temperature and
Tensile testing Samples: Three samples of each alloy; bulk solder provide all eight graphs.
samples with round gauge sections between 2 mm to
5mm in diameter and gauge length of 50 mm. Geometry Report sample gauge diameter in mm.
and testing conditions must be identical for all samples.
Density Direct measurement of volume and mass None Density (p) in g/cm
3
Vickers hardness As per test method None HV [dimensionless]
ASTM E92-82(2003)e2
Coefficient of thermal expansion Test condition: Measurements taken every 25°C from SAC305 Graph of thermal expansion (ppm/ºC) versus temperature (ºC) for
(CTE) 50°C to 200°C, averaged for the three tests of each solder new alloy and SAC305. Provide the standard deviation for each
TMA as per ASTM E831-06 alloy data point (as error bars), along with the averaged values at each
Samples: Three samples of each alloy, 10 mm in length, temperature.
lateral dimensions not to exceed 5 mm.
Ramp rate: 10°C/min. Report average CTE between -50°C to200°C in ppm/ºC for each
alloy.
Report sample shape and dimensions.
16 – Global SMT & Packaging – November 2008 www.globalsmt.net
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