A study about 3D stacking of passive SMD elements for advanced SMT packaging using laser assisted bonding

This study demonstrates laser assisted bonding (LAB) of SMD Tantal Elko and MLCC (Multilayer Ceramic Chip Capacitor) capacitors and presents a comparison to conventional bonding using solder paste and reflow oven. The LAB technique, unique to Pac Tech, has greatly improved ensuing properties of packages over conventional oven reflow processes. As the LAB process is temperature controlled, it allows for a non-destructive yet fast and minimally invasive reflow of the bond-layer (solder). While the LAB process was demonstrated previously in terms of a wide range of applications, its feasibility and advantages have not yet been assessed for the stacking of passive SMD elements such as capacitors or resistors [1]-[3] and [4]. In this study, the 3D stacking possibilities of SMD capacitors will be evaluated. This technique allows the vertical or horizontal arrangement of the SMD elements on top of each other. The overall footprint of a given device such as a capacitor can be reduced, as it can be replaced by a stack of two or more smaller devices. To evaluate the potential of the LAB process, several sizes of SMD capacitors (3216M, 2012M and 1005M) were bonded and stacked. A parametric study was performed to evaluate suitable process windows for a given number of samples. To analyze test assemblies, several techniques were employed such as microscopic inspection, electrical qualification, 3D surface scans, shear-test and cross-sectional analysis. The robustness of the assemblies was investigated via a vibration test. Specifically, the mechanical properties of the devices were simulated through several cycles of high frequency vibration tests relative to three-dimensional loads. Finally, future perspectives regarding potential applications of passive SMD element stacking and LAB SMD assembly are elucidated.