Pen-Shan Chao

High density vertical probe card fabrication with low cost and high precision characteristics by using MEMS process

The goal of this paper is mainly to develop an advanced MEMS probe card, which combines not only microelectroplating but CMP (chemical mechanical polishing) processes to manufacture a kind of spring-like probe. It is characterized by providing great deformation in its vertical axis (Y-axis). Apart from those specific technologies, finite element simulation software, COSMOS, is also employed to analyze the loading force distributed on the probe tip. Compared to the traditional drawing process, these MEMS based process is expected to have more flexible in probe design. Also, this process using batch mode fabrication method is also conducive to reduce the entire fabrication cost. We can reach the outstanding targets as following, hardness higher than HV 550, Youngs modulus higher than 180 GPa, fatigue strength higher than 1 million times, maximum loading force about 4 g, and electric resistance less than 10 muOmega-cm

Fabrication of a MEMS-Based Cobra Probe

This study presents a new type of cobra probe by using MEMS technology for IC testing. The fabrication includes photolithography, electroforming and polishing process. Mechanical properties of the cobra probe are measured and no fracture or deformation is found after applying a force of 3 g for as many as 20,000 times. Its contact resistance averages nearly 680 mOmega and overdrive is approximately up to 30 um.

Fabrication of high density and high conplanarity lead-free solder bump by a novel process for advanced wafer level packaging

This paper aims to provide a fine-pitch Sn/0.7Cu lead-fee solder bumps fabrication process that is characterized by using a novel plating-friendly polishing mechanism to transform the plated-based Sn/0.7Cu lead-free solder bumps with huge height deviation into smooth and uniform ones. The final experimental results showed that the UIW (uniformity in wafer) of Sn/0.7Cu solder bumps at 50 mum pitch size could be sharply decreased from 9.19% after plating to 3.54% after polishing and even 1.9% after reflow throughout the entire 4 inch silicon wafer. Most importantly, after reflow uniformity could be controlled as accurately as within 1.25% in each dies (10 mm times 10 mm) respectively. This proposed polishing mechanism could assist the plating-based fine-pitch solder bumps in precisely getting better coplanarity so as to enhance packaging reliability and yield.

Using an Innovative Polishing Process to Fabricate Ultra-High Uniformity of Polymer Surface

Commonly used in forming high aspect ratio structures, thick-layer polymers generally differ in surface uniformity due to relatively higher viscosity. This problem would become even worse along with the increase of substrate diameter. Non-uniform coated photoresist surface would cause bonding failure and dimensional error in advanced three-dimensional packaging and WLP (wafer level packaging). Using traditional CMP (chemical mechanical polishing) to polish such a huge height deviation is time-consuming, high-cost and low-efficiency. This paper aims to provide an innovative polishing mechanism that is particularly suitable to polish wider height deviation in microstructures. Predominately in mechanical polishing force entails it surpassing CMP in MRR (material removal rate) by 300 times. The final experimental result indicates that the polishing rate could reach as fast as 20 um/min. Most importantly, the whole uniformity after polishing could be sharply decreased from 105plusmn3 mum (uniformity: 2.8%) to 95plusmn1 mum (uniformity: 1%). This proposed polishing mechanism could assist sticky polymers in precisely getting better uniformity so as to enhance packaging accuracy, reliability and yield.

Development of CMOS Process Compatible Force Sensor and its Application to Probe Card

This thesis aims to apply a standard CMOS process to develop a Wheatstone-bridge- based piezoresistive force sensor. This CMOS-compatible piezoresistive force sensor with small area and easy fabrication consists of a thin-film receiver made by passivation, silicon oxide and a piezoresistive layer made by the polycrystalline silicon respectively. Additionally, utilize the RLS etching process offered by CIC to conduct its post-process. Combining MEMS with the electroforming process enables us to fabricate vertical spring probes featuring strength feedback function, making it possible to monitor wafer-level probe card either on-line or off-line. In traditional, the working probe naturally sustaining repeated bending actions and wear, absolutely needs a mechanism to prevent it from being damaged, caused by the change of the probes geometry and the increase of the contact resistance. Therefore, in this study, we develop a CMOS-based chip in connection with the electroformed probes to detect each of their counterforce, contact resistance to evaluate if their contact force and coplanarity are controlled within safe range. This breakthrough technology of installing a piezoresistive force sensor to fully monitor the working probe cards helps to save time and manpower for broken probes repair.