Could application of column-grid-array (CGA) technology result in inelastic-strain-free state-of-stress in solder material?

Abstract

Physically meaningful and easy-to-use analytical stress model is developed for a short cylinder (beam) clamped at the ends and subjected to bending caused by the ends offset. The offset is due, in its turn, to an external lateral force that has to be determined from the known offset. It is envisioned that such a beam can adequately represent the state of stress in a column-grid-array (CGA) solder joint interconnection experiencing thermal loading due to the thermal expansion/contraction mismatch of the IC package and the printed circuit board (PCB). The CGA designs are characterized by considerably higher stand-off heights than ball-grid-array (BGA) systems. The offset D = lDaDt for a CGA solder joint located at the distance l from the mid-cross-section of the package/PCB assembly (the neutral point (DNP)), can be determined, in an approximate analysis, as a product of this distance and the ''external'' thermal mismatch strain DaDt between the IC package and the printed circuit board (PCB). Here Da is the difference in the effective coefficients of thermal expansion (CTE) of the PCB and package materials, and Dt is the change in temperature. The objective of the analysis is to demonstrate that the application of a CGA design, in which the solder joints are configured as short clampedclamped beams, enables one not only to significantly relieve the thermally induced stresses, compared to the BGA system, but possibly to do that to an extent that the stresses in the solder material would remain within the elastic range. If this is achieved, the low-cycle-fatigue condition for the solder material will be replaced by the elastic-fatigue condition, thereby leading to a significantly longer fatigue lifetime of the joint. The elastic fatigue lifetime can be assessed, as is known, based on the Palmgren-Miner rule of linear accumulation of damages. Our analysis is limited therefore to elastic deformations.

Influence of Manufacturing Mechanical and Thermal Histories on Dimensional Stabilities of FR4 Laminate and FR4/Cu-Plated Holes

“…New materials with better properties were developed to lower the residual thermal stress. Hart [13] recommended replacing spherically-shaped balls with cylindrically-shaped solder columns to decrease the CTE mismatch during microelectronics assembly (the limitations of this approach were discussed elsewhere [14]). Chung et al [15] performed thermomechanical analysis of PCBs during the reflow process for warpage prediction.…”

Inhomogeneous Bonding in Low-TemperatureSoldering: Brief Review

“…If this happens, the low-cycle fatigue condition will be avoided, the elastic stresses and strains will occur, and, owing to that, the lifetime of the solder joints will be much longer. It is noteworthy that the above results were obtained using analytical modeling [19][20][21][22][23][24][25][26][27][28][29][30][31][32] and, in the majority of cases, confirmed by FEA. Future work should be focused therefore mostly on experimental investigations and, particularly, on accelerated failure-oriented accelerated testing (FOAT) [33][34][35][36][37], to compare, for different package designs, the performances and lifetimes of conventional, homogeneous, and inhomogeneous designs.…”

Flip-Chip (FC) and Fine-Pitch-Ball-Grid-Array (FPBGA) Underfills for Application in Aerospace Electronics—Brief Review

“…Pioneering publications [54][55][56][57] addressed materials, mechanics, and reliability of solder joints for surface mount electronics. Analytical thermal stress modeling [58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] was applied to predict the magnitude and the distribution of thermal stresses and provide recommendations for preventing thermal stress failures in IC packages, including those with solder joints. It was shown particularly [60][61][62][63] that by employing solder joints with elevated stand-off heights, one could provide considerable stress relief in the solder material.…”