Tan, Chew Pheng
(2006)
Determination Of Fracture Toughness
In PBGA Packages Using Finite Element And
Experimental Methods.
Masters thesis, Perpustakaan Hamzah Sendut.
Abstract
Electronic packages especially the plastic ball grid array (PBGA) has its
unique crack failure arising from the soldering process. The existence of
moisture absorbed in package from ambient condition causes vapor pressure.
During reflow soldering processes (215°C), the moisture absorbed vaporizes
and eventually causes popcorn cracking. So, numerical method is used to
characterize the fracture resistance in terms of geometric stress intensity factor
(SIF). Then, the investigation of fracture toughness on epoxy molding
compound (EMC) material provided boundary conditions of package cracking.
In this research, Ansys software was used to simulate moisture diffusion
and thermal transfer to determine the vapor pressure at the crack region. The
vapor pressure loading was applied on PBGA to obtain geometric SIF using
modified crack closure integral (MCCI) method. It was found that the increased
in vapor pressure and higher delamination size created high geometric SIF.
Load-crack edge extension relation obtained from holographic interferometry
(HI) method and critical load for D.E.R. 331 as EMC material were used to
evaluate fracture toughness. The fracture toughness for D.E.R 331 was found
to be 0.488MPa m 1/2.
Eventually, the fracture toughness for D.E.R. 331 was compared with
PBGA's geometric SIF. A graph with package safety conditions was obtained.
From the graph, it can be concluded that the PBGA is typically to be saved
during soldering process, where vapor pressure is 1.21 MPa and delarnmatron ratio is less than 0.6. This EP's failure can be controlled through minimizing the
effect of vapor pressure and reducin_g die/EMC interface delamination.
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