B-staging of toughened epoxy composites

by Fred Arnold and Steve Thoman

Elgin BravoFebruary 09, 2001

Overview of B-stage process for LLP

• Reduce package size by wirebonding close to the edge of the die.

• Backcoat wafers with a B-stage epoxy.

• Delamination of die from DAP due to high humidity and temperature.

• Understand structure and properties of epoxy.

About the authors

• Fred Arnold and Steve Thoman affiliated with Naval Air Warfare Center

• Polymers and Composite branch.

• 28th International SAMPE conference Seattle WA, 1996

Objectives

• Characterize cure behavior and glass transition temperature of Hercules 8552 sulfone toughened B-stagable epoxy.

Definition of B-staging

• To cure an epoxy to a pre-determined degree of chemical conversion.

• Stage o Chemical conversion

• Green 0• B-stage <0.29• C-stage <0.90

Equipment• Dynamic Mechanical Analyzer (DMA)

– glass transition– secondary transitions– gelation– vitrification

• Differential Scanning Calorimeter (DSC) equipped w/ modulated DSC cell (MDSC)– specific heat capacity – heats of transition – temperature of phase change

Experimental

• Sample size:• 3-5 mg for resin• 25-35 mg for B-staged

• Heating rate• 3oC/min

• Modulation frequency• 0.5oC

Glass transition temperature

MDSC results compared to DSC

Tg of green epoxy at 23oC

T(t) = To + Bt dQ/dt = CpB + f(t,T)

Tg as a function of conversion

Conversion and Isothermal cure

Results

• MDSC produces more accurate results

• Reversing component eliminates effect of residual heat release near Tg

• Optimum B-stage temperature obtained to ensure mechanical strength at RT

Research comparison

• Understand Tg using DSC• Degree of chemical rxn for B & C stage• Die delamination

• MDSC not available