ELECTRONIC ASSEMBLY WITH ENHANCED THERMAL DISSIPATION THANKS TO A METALLIC BONDING LAYER COMPOSED OF SOLDER AND COPPER

An electronic assembly (111, 211, 311) comprises a semiconductor device (14) with a first side (42) and a second side (44) opposite the first side (42). The first side (42) has a first conductive pad (34). The second side (44) has a primary metallic surface (22, 122). A first substrate (e.g. lead frame) (10, 110) is bonded to the first conductive pad (34) via a first metallic bonding layer (12, 112). A second substrate (e.g., heat sinking circuit board) (18, 24) is bonded to the primary metallic surface (22, 122) via a second metallic bonding layer (16, 116). The first and second metallic bonding layers (12, 16, 112, 116) are composed of solder or of solder and copper, e.g., copper particles, copper flakes, copper pellets or copper fillers, wherein the copper pellets may be coated with a solderable finish such as tin, silver or electroless nickel immersion gold (ENIG). In the first bonding layer (12), the second bonding layer (16) or both, the copper content can facilitate enhanced heat dissipation from the semiconductor device (14), can promote improved thermomechanical strength of one or more bonding layers (12, 16) and can reduce mismatch and associated thermal stress resulting from a difference in coefficients of thermal expansion of the semiconductor device (14) and the first substrate (10) (e.g., lead frame) or secondary substrate (18) (e.g., heat sink). The first metallic bonding layer (12, 112) may be arranged as a first matrix of islands of solder. The lead frame (10, 110) may have a substantially planar portion (46) having a lower surface for interfacing with the first conductive pad (34) on the semiconductor device (14) and having an upper surface for coupling or receiving, directly or indirectly, a first heat sink (20). The substantially planar portion (46) of the lead frame (110) may comprise holes (54) serving as solder outgassing outlets and also allowing for the creation of an array of solder fillets on the surface of the lead frame (110) at the end of soldering. The first side (42) of the semiconductor device (14) may have the first conductive pad (34), a second conductive pad (38), and a third conductive pad (40). The second side (44) of the semiconductor device (14) may comprise the primary metallic surface (22) and a secondary metallic surface (23), where the primary metallic surface (22) and the secondary metallic surface (23) are spaced apart and separated by a dielectric region (45) or dielectric barrier. Alternatively, the primary m