Influences of pad shape and solder microstructure on shear force of low cost flip chip bumps

Jian Cai, Simon Law, Annette Teng, Philip Ching Ho Chan

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

12 Citations (Scopus)


The bumping process plays a critical role in flip chip technology. A low cost bumping process has been developed using electroless nickel and immersion gold followed by stencil printing. The process flow is described in this paper. The Al pad size is about 100μm in diameter with a pitch of 400pm. Different electroless plating solutions were evaluated as well as different solder pastes were used to evaluate the stencil printing process. Also different pad shapes were tested for shear strength. Ni studs with no bump material were fabricated to evaluate the electroless process. The shear force test result shows a strength value of 230MPa for Ni stud. The solder bump after reflow has a diameter of 160μm and a height of 120μm. There is some difference in the shear force test results for different pad shapes. SEM and ED AX results of the fracture surface indicate that the fracture was cohesive or inside the solder. Cross sections showed some intermetallic layers at the interface. A Ni-Sn intermetallic layer and a phosphorus rich layer formed during reflow, which has a composition of Ni3Sn4 and Ni3P respectively. The low cost flip chip samples were subjected to multiple reflows and shear force tests were performed. Fracture surfaces were analysed and failure modes were differentiated.
Original languageEnglish
Title of host publicationInternational Symposium on Electronic Materials and Packaging, EMAP 2000
Number of pages8
ISBN (Electronic)0780366549, 9780780366541
Publication statusPublished - 1 Jan 2000
Externally publishedYes
EventInternational Symposium on Electronic Materials and Packaging, EMAP 2000 - Hong Kong, Hong Kong
Duration: 30 Nov 20002 Dec 2000


ConferenceInternational Symposium on Electronic Materials and Packaging, EMAP 2000
Country/TerritoryHong Kong
CityHong Kong

ASJC Scopus subject areas

  • Engineering(all)

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