US EPA

2169192 

Journal Article 

Bending fatigue characteristic of Sn-3.5Ag solder bump on Ni-UBM 

Kang, KI; Jung, JP; Bang, WH; Park, JH; Oh, KH 

2008 

1 

Materials Science Forum
ISSN: 0255-5476
EISSN: 1662-9752 

MATERIALS SCIENCE FORUM 

580-582 

177-182 

10.4028/www.scientific.net/MSF.580-582.177 

WOS:000258372000043 

Bending fatigue behavior of eutectic Sn-3.5Ag solder bump bonded oil FR4-PCB was characterized by experimental and finite element method (FEM). To investigate all effect of stress state oil bump failure, which had not been weighed in conventional Coffin-Mall soil model of N-f=K.Delta epsilon(-1 similar to-2)(p), 'fatigue frequency variable' and 'bump viscoplasticity' were included in analysis procedure. As experimental results, with increasing fatigue cycles from 3,000 to 10,000, bond strength decreased from 98.9% to 76.5%, and from 97.5% to 67.1% at the fatigue frequencies of 2.5Hz and 5.0Hz, respectively. Stress state could be critical components to determine fatigue life, which should be combined in Coffin-Manson criteria. FEM calculation showed that higher bending frequency led to higher normal stress development at the solder and IMC interface, but smaller plastic strain in bump. However, bending fatigue experiment revealed discrepant results from that or Coffin-Manson criteria. Higher bending frequency, which was predicted to give rise to smaller Delta epsilon(p) at solder, showed dramatic bond deterioration of solder bump on UBM (under bump metallurgy). This was confirmed experimentally through SEM (scanning electron microscopy) observation as cracks were found at the solder bump and UBM interfacial IMC, Ni3Sn4, in case of the higher bending frequency. 

bending fatigue; Sn-3.5Ag solder; microstructure; Coffin-Manson model; stress state