Ceramic column grid array technology with coated solder columns

Flip-chip carriers are finding increasing use for high-performance ASIC and microprocessors chips. Many of these chips have a large I/O count and consequently drive chip carriers with high density second-level interconnection requirements (typically 400 to more than 1000). IBM has a range of Ceramic Ball Grid Array (CBGA) and Ceramic Column Grid Array (CCGA) offerings which cover this application range. In this paper, we describe the development of a new CCGA technology with coated solder columns which allows column attach at the very end of the module assembly process. The new approach developed was to make Pb90-Sn10 solder columns with a thin barrier layer which are joined to the module I/O pads using a lead-free Sb5-Sn95 solder preforms. The barrier layer prevents the reaction of Sn/Sb with the Pb-rich column and driving the interface towards the Sn/Pb eutectic phase with its low melting point of 183°C. As a result, during card assembly and rework of the module from the card, the column joints on the ceramic substrate do not melt. The coated CCGA structure has two beneficial attributes: being able to join to the module at the end of the module assembly (as in CBGA process), and the ability to remove the CCGA module from a card with all the columns attached to the module (like the cast CCGA structure). In this paper, the structure and attachment process of the coated CCGA and the reliability of coated CCGA connections to an organic FR-4 card are reviewed. A nonlinear finite element modeling has been carried out to study the resistance to cyclic viscoplastic deformation and related damage mechanism. A deformation-base lifetime analysis method was used for the column fatigue life prediction and was compared with the actual test data