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CCGA Solder Column - Reliable Solution for Absorbing Large CTE Mismatch
Keywords: Column Grid Array, Micro-Coil Spring, CCGA
Assembling printed circuit boards (PCB) with commercially available plastic Ball Grid Arrays (BGA) is an accepted industry practice. In most cases, solder ball interconnections between a plastic BGA and PCB perform reliably well. Not so with large sized Ceramic Ball Grid Array (CBGA) typically found in mil/aero/defense applications. Solder balls encounter large stresses due to the inherit mismatch of the material's coefficient of temperature expansion (CTE) between a ceramic CBGA module and a plastic FR4 (or polyimide) circuit board. The array of solder balls are stretched and squeezed 2.5mils (63um), or more, from corner to corner under a 45mm square CBGA field programmable gate array (FPGA), as the temperature swings 1000C from hot to cold in repeated cycles, typically encountered in harsh operating environments. While this amount of travel seems small - about the thickness of a single sheet of paper - such movement ultimately leads to catastrophic failure as solder balls delaminate from the PC board and/or the CBGA. The solution for overcoming CTE mismatching is to replace solder balls with solder columns, making a device known as a Ceramic Column Grid array (CCGA). Solder columns are compliant and easily absorb stresses caused by stretching and pulling in applications involving high vibration, shock and varying temperatures. CCGA have been used for decades by well known chip makers such as IBM, Xilinx, Atmel and (Actel) Microsemi, just to name a few. This presentation covers several types of column solutions that are commercially available such as plain Pb90/Sn10 columns, copper wrapped Pb80/Sn20 columns, NASA Micro-coil Spring, and interposer columns. This presentation explains the use and discusses issues associated with columns facing large temperature swings, how to absorb stresses from CTE mismatch, how to select the optimum column interconnect, whether copper ribbon columns or high shock and PCB deflection test results of the Micro-coil Springs, and effects from different sizes of Micro-coil springs. This presentation will also take a forward look at several new types of columns in development and address how to attach columns to both ceramic and plastic packages. Keywords: CCGA, column grid array, solder columns, Micro-Coil Spring, Pin-Pack
Martin Hart,
Irvine, CA

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