Ultra-Thin HDI Multi-Purpose Test Vehicle Paper SMTAi September 2016


In the last decade, the Ultra-Thin HDI (High Density Interconnect) technology has dominated the mobile/wearable products designs, yet the standard test vehicles used for qualifying materials, components and connectors provided by IPC (Institute of Printed Circuits), ANSI (American National Standard Institute) and JEDEC (Joint Electron Device Engineering Council aka Solid State Technology Association), are obsolete and OEM’s (Original Equipment Manufacturer) have stopped using them. These test vehicles do not reflect the form factors, density and interconnect methods used by the industry. In addition, they do not capture failure modes of the fine pitch BGA (Ball Grid Array) technology and as a result don’t provide upstream Users adequate data for development.

Microvias and dielectrics are the key, along with finer lines and spaces, in obtaining the density of Ultra-Thin HDI boards. Continuous reduction in PCB dimensions and feature sizes challenges both fabrication process and test vehicles. HDP User Group’s paper gives a brief introduction to the modern Ultra-Thin PCB (Printed Circuit Board) fabrication process.  It discusses typical board level reliability tests and presents a generic reliability test vehicle design which is based on current Ultra-Thin HDI technology. With the proposed test vehicles’ design of modularity and scalability it is easy to modify to meet the next generation of Ultra-Thin HDI PCB requirements. The study indicates that the proposed TV design covers HDI test requirements and most of the current tests are critical when evaluating modern Ultra-Thin HDI circuit board reliability.

The HDP User Group project also conducted a study on the application and reliability of a very fine pitch WLCSP (Wafer Level Chip Scale Package) on this Ultra-Thin HDI test vehicle. A 0.3mm pitch WLCSP daisy chain, commercially available solder paste, flux and underfill were used for this study. The details of the assembly process including solder paste printing, dip flux, component placement, reflow and underfill dispensing are discussed. The impact of the test vehicle OSP (Organic Surface Protection) surface finish on the assembly process and result is addressed as well. JEDEC standard air-to-air thermal cycling and drop tests are performed for reliability evaluation purposes. The reliability data of solder paste printing vs. dip flux, underfill vs. non-underfill are compared and evaluated. All results show that the WLCSP application process and materials on the ultra-thin test vehicle are robust and reliable.