Jan/Feb, 2024 Continued from page 58
spacing, is usually less than a PBGA, some- times down to as little as 0.5 mm or 0.02 in. Therefore the re-balling process is a little more difficult than standard BGAs, however all the same process parameters apply. Micro BGAs and CSPs are also subject to moisture absorption and related defects and the neces- sary precautions outlined above should be taken.
The ceramic BGA package employs a
“flip-chip” technology where an actual chip is bonded to the top of a fired ceramic substrate using a technology pioneered by IBM called “C4”. C4 is an acronym meaning “controlled collapsible current conductor.” CBGAs use an array of 0.035 in. (0.89 mm) diameter
SN10/PB90 solder balls which have been joined to the bottom of the ceramic substrate using eutectic solder.
In the re-balling process of a 1,000 I/O package, if just one ball size is incorrect (a 99.9% accuracy), the rework will look good but will not work properly.
During reflow the eutectic
solder at the ball/substrate and the ball/PCB complete the electromechanical connection. Hence, it is required to screen solder paste onto the PCB land pattern or onto the high-temper- ature solder balls to facilitate the bond. The high melting point sol- der balls do not reflow, but instead maintain a 0.035 in. standoff between the substrate and PCB. These types of connections
provide the required flexure to accommodate the thermal coeffi- cient of expansion (CTE) mis-
Fine-Pitch Direct Die Attach...
Continued from page 59 In concept this z-axis mag-
netically aligned conductive epoxy approach could integrate multiple silicon wafers on top of each other, creating the possibil- ity for an exceptionally dense integrated system-in-package (SIP). Processing temperatures can be as low as 176°F (80°C), opening room for alternate sub- strates
and biocompatible
assemblies. This anisotropic epoxy is not limited to specific device attachment; it can be used to bond multiple component sizes and styles across an entire sub- strate.
Contact: SunRay Scientific,
22 Meridian Road, Suite 1, Eatontown, NJ 07724 % 732-443-4807 E-mail:
johny@sunrayscientific.com Web:
www.sunrayscientific.com r
See at IME West, Booth 4230
www.us -
tech.com Trends in BGA/CSP Reballing...
match between the ceramic substrate and the PCB.
Finally, The ceramic column grid array
(CCGA) is a variation on the CBGA in that instead of using non-eutectic high tempera- ture solder balls it employs solder columns measuring 0.020 in. in diameter and between 0.05 and 0.087 in. in height. These solder columns are designed to
provide greater flexure to accommodate high power dissipation levels. Re-balling is not recommended for these package types due to their extreme complexity. However, due to the high cost, it may prove to be cost effec- tive, even with the longer processing time and lower yield. Contact: APEX Tool Group, 670
Ceramic ball grid array.
Industrial Drive, Lexington, SC 29072 E-mail:
rich.matthews@
apextoolgroup.com Web:
www.weller-tools.com r
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