Effect Of CuCF Composite Properties On Residual Stresses In Brazed CuCF/GaAs System
Dariusz Kaliński Instytut Technologii Materiałów Elektronicznych, ul. Wólczyńska 133, 01-919 Warszawa
Annals 1 No. 1, 2001 pages 83-85
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abstract The paper presents the results of calculations, performed using the finite element method (FEM), which include a comparative analysis of the residual stress state induced in the GaAs laser diode (DL)/heatsink (OC) joint systems (Fig. 1) that differed from one another in the material used for the heatsink (Cu, CuCF) (Tab. 1). This analysis permitted us to test the materials examined in terms of the level and distribution of the residual stresses developed in the system. The calculation results show, that in the model with the CuCF composite the maximum level of the tensile stresses generated in GaAs (σMAX-SMAX) is about 6 times lower (SMAX = 3.31 MPa) than that in the systems with a conventional copper heatsink (SMAX = = 21.0 MPa) (Fig. 2 and Tab. 2). We also observe a considerable difference in the level and distribution of the axial stress Sx (Fig. 3). Within the semiconductor device, the values of this stress component are negative (compression). In the copper heatsink system, the magnitude of Sx varies from about −325.0 MPa at the central region of GaAs (x = 0.0, y = 0.01) to 0.0 MPa at its outer wall (x = 6.0, y = 0.01) (Fig. 3). In the CuCF/GaAs system, the stress Sx remains almost constant and ranges from −4.5 to −6.0 MPa (Fig. 3). For comparison, Fig. 4 shows the principal stress curves SMAX in Cu/GaAs model system, soldering using SnPb40 alloy (Tab. 1, heat load 450⇒293 K). In this case extreme magnitude of tensile principal stress SMAX in GaAs is about 4.5 times higher (SMAX = 15.52 MPa) than that in the systems with the composite CuCF heatsink, even jointed AgCu28 braze alloy. This advantageous reduction of the stress level is due, among other factors, to the decreased difference between the values of the thermal expansion coefficient of the CuCF composite and GaAs (Δα = 0.5 ⋅ 10−6 1/K) compared to the difference that occurs in a system with a copper heatsink (Δα = 11.3 ⋅ 10−6 1/K).