A Method for SMT Compatible Assembly of Ultra-Thin Die to PWB using a Release Tape with an ACF Planarizer
Original Publication Date: 2001-Feb-21
Included in the Prior Art Database: 2001-Feb-21
Krishna Kalyanasundaram: AUTHOR [+3]
AbstractA Method for SMT Compatible Assembly of Ultra-Thin Die to PWB using a Release Tape with an ACF Planarizer
A Method for SMT Compatible Assembly of Ultra-Thin Die to PWB using a
Release Tape with an ACF Planarizer
By Krishna Kalyanasundaram, Daniel Gamota, Steve Schiefers and Andrew Skipor
Lower semiconductor package thickness and less weight are among the significant benefits of using ultra-thin die. The methodology used today to assemble circuits with ultra-thin die is both time and labor-intensive. A high-volume-compatible tape and reel solution for assembling circuits with ultra-thin die is proposed.
Reduction in wafer thickness has increased the opportunities for miniaturization of portable electronics. Ultra-thin die provide the same functionality of standard thick die, while allowing for reduction of semiconductor package thickness and weight. The current methodology to handle ultra-thin die consists of attaching a thick piece of silicon to the backside of the fragile ultra-thin die that acts as a planarizer and as a rigidizer. The ultra-thin die with the rigidizer is attached to the substrate using a standard pick-and-place machine and the silicon rigidizer is removed by applying heat and torque (Fig. 1). This methodology is slow and does not meet the cycle time demand that is typical of high-volume manufacturing. Further, this methodology requires additional equipment and manufacturing floor space. This, in turn, requires modification of a standard SMT assembly line resulting in increased cost.
The ultra-thin die is packaged in a tape and reel form at the wafer fab (Fig 2) where it is placed bumps-up on a release film A that is coated with a low-strength adhesive. An Anisotropic Conducting Film (ACF) is then placed on top of the ultra-thin die. A release film B is then placed on top of the ACF and this constitutes the ultra-thin die-ACF composite reel. This reel is shipped to the final manufacturing facility.
The release layer B is peeled to expose the ACF at the placement module at the final manufacturing facility (Fig 3). The fiducials on the composite reel are used to align the position of the composite to the substrate. The placement/thermo-compression bonding head applies heat and pressure to the release layer A and this simultaneously transfers and bonds the ultra-thin die-ACF composite to the substrate.
Fig. 1. Current Method to Assemble Ultra-thin Die.