Assessment of Die Attach Film for Thin Die and SiP Applications
The drive for package miniaturization and die thickness reduction has created new challenges for conventional die attach paste materials. Die attach film (DAF) is seen as a potential candidate especially in applications requiring die thickness =100 mum. However, processing of DAF materials also presents certain difficulties especially in dicing of DAF-laminated wafers. This paper outlines the challenges and process optimization carried out for 5 different DAF materials. Process feasibility study and dicing optimization were conducted on 100 mum thick wafers. Subsequently the DAF materials were assembled into a ball grid array (BGA) package and subjected to reliability testing (Moisture Sensitivity Level 3, Unbiased Highly Accelerated Temperature and Humidity Stress Test and Temperature Cycling). Results showed that minimum chipping and whisker formation can be achieved using a 2-step dicing process with optimized cutting depths and feed rate. It was also found that optimum adhesion of the DAF material to both the dicing tape and die backside is necessary to prevent "flying die" during dicing and die pick-up problem during die attachment. Positive results for 2 DAF materials were obtained from reliability performance assessment. These findings show that there is a robust DAF material and process for thin die and System-in-Package (SiP) applications.
Wafer sawing process characterization for thin die (75micron) applications
The drive for package thickness reduction has created new processing challenges with regards to thin wafer handling. While back-grinding and die attach film (DAF) lamination are now established procedures, sawing DAF-laminated wafers with wafer thickness 3 mils and below is still a significant challenge. The need is for a suitable saw process that meets the following criteria: less than 1 mil wafer chipping, low cost and high throughput. This paper elaborates work that evaluated different saw parameters and their effects on wafer chipping. 8" wafers with varied die sizes and 2 in 1 DAF-dicing material sets were used during this evaluation. The work evaluated both single and dual pass saw processes. The effects of saw parameters-feed speed, RPM and blade types are also elucidated. The results show that for thin die a dual pass saw process gives better results than a conventional single pass process. Results also show that using non-optimized saw process parameters for a given DAF material set combination could adversely affect the yield consequent assembly processes like die attach and wirebond.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.