Development of large die fine pitch flip chip BGA using TCNCP technology

Abstract

Recently, technologies related to Fine Pitch Flip Chip or FPFC have been great achievements for various next generation devices, allowing a significant increase in the number of signal I/O and achieving low form factor packages. Consequently, fine pitch Cu pillar flip chip Chip Scale Package (CSP) with small sized die, with package dimension of less than 16×16mm, is already under high volume production using the Thermal-Compression Bonding with Non-conductive Paste (TCNCP) technology [1–2]. In the case of Flip Chip Ball Grid Array (FCBGA), there is a growing need for FPFC technology with Cu pillar in supporting next generation silicon node. However, there will be a high possibility of yield drop issue in conventional mass-reflow process and potential reliability due to the highly concerned tensile stress between low k die and substrate by CTE mismatch especially at the edge of the die. This can be a critical quality issue for fine pitch devices compared to normal pitch (i.e., 150um) flip chip BGA. Therefore, TCNCP bonding as an alternative should be studied on fine pitch Cu pillar flip chip BGA. This paper will discuss fine pitch flip chip assembly technology for large sized flip chip BGA. Two kinds of assembly method, mass reflow bonding versus thermal compression bonding, for the flip chip bonding will be compared for the large FPFCBGA package. Meanwhile, the advantage of TC bonding with pre-applied underfill process will be described. For robust interconnection between die and substrate for large FPFCBGA, the result of the bonding test will be described with several surface finishes such as ENEPIG, Direct Immersion Gold (DIG), Immersion Tin (IT), and Solder Coating on substrate. Interestingly, one of selected surface finishes has shown excellent reliability test results. Finally, this paper will discuss an effective approach for fine pitch devices from an assembly perspective.