16° 21°14°

42° 17°52°

18° 18°

48°

Crack development in lead-free solder in PGBA packagedue to recrystallization that forms ‘red’ orientations

Thomas R. Bieler, Michigan State University, DMR 1006656

SAC 305 lead-free solder joints on PBGA package

pre-aged 100°C/500hrs 6400 0~100°C thermal cycles

C-axis OIM map

• Prior research indicates ‘red’ orientations ( [001] parallel to interface) susceptible to cracking

• Bulk orientations are not accurate indicators of whether joint cracks in this package.

• Fine step EBSD scans near interface show ‘red’ orientations highly correlated with cracking resulting from continuous recrystallization.

• Mechanism of continuous recrystallization depends on activated slip systems that will be analyzed in the coming year

Cross-polarized light image

In-situ synchrotron X-ray characterization of lead-free solder;melting, dissolution and resolidification kinetics are quantified…

Thomas R. Bieler, Michigan State University, DMR 1006656

• (a)(b): Melting process; (c)(d): Resolidification• Melting and solidification occurs

in about 0.5-1s, but complete melting of Sn and dissolution of IMCs can take 3-30 seconds.

• Cu6Sn5 IMC remains with no dramatic change during the melting and solidification process.

• Co-existence of molten Sn and earliest formed Sn nuclei are evident in (c, d, arrows).

• Each reflow results in different crystal orientations, (a) vs. (d).

• First proof of what has been speculated by scientists and manufacturers for years

806.5 s~219°C

923s~195°C

922.5s~195°C

810 s~224°C

(a)

(d)

(b)

(c)

Sn

Cu6Sn5

Cu

Ag3Sn

Ni3Sn4

SAC-305 lead-free solder balls in a Wafer-Level-Chip-Scale package

Integrated diffraction patterns from ball and interface metallurgy

Liquid Sn broad peak

Si

Si

Liquid Sn broad peak

1.15 1.35 1.55 1.75 1.95 2.15 2.35 2.55 2.75 2.95 3.15

D-spacing(A)

(200)(110)(111,021)

(113)

(101)

(101)

(211)

(200)

(301)(321)(220)

(312)