RF and Mechanical Evaluation of Low-Cost Polymer Substrate for High Frequency Flip-Chip Packaging

• Main Authors: Oh Chee Way, 胡志偉
• Other Authors: Edward Yi Chang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/01267719481313905245

碩士 === 國立交通大學 === 材料科學與工程系所 === 97 === This work studies the selection and evaluation of new board materials RO3210 that enables flip chip packaging in microwave applications. A coplanar transmission line structure on GaAs chip were mounted on a RO3210 substrate using flip chip Au-to-Au thermal compression method. By using suitable layout optimization and compensation design, the S parameters performance of this structure was greatly improved. From DC to 67 GHz measurements, the resultant reflection loss S11 and insertion loss S21 exhibited excellent performance of -20 dB and -0.8 dB respectively. These results agreed well with the EM simulation data. Meanwhile, the flip chip bonding of in-house fabricated m-HEMT active devices on RO3210 also displayed excellent gain performance by small deviation -2 dB. Besides, the influence of encapsulant (underfill/ glob top) was also investigated. When epoxy resin encapsulant was injected into flip chip structure, the frequency band of the devices shifted to low side. To extend the use of this encapsulation method to high reliability and harsh environmental conditions, thermal cycling (-55 °C to 125 °C, 600 cycles) and humidity test (85 % RH/ 85 °C, 500 hours) were carried out. The effect of board properties such as coefficient of thermal expansion (CTE) upon the reliability performance was investigated. Glob top encapsulation which found widespread acceptance in electronics assembly for low frequency packaging consumer products (wire bonding type packaging) showed poor performance as a result of large CTE difference between the board and encapsulant (completely failed at 200 cycles). Meanwhile, packages with underfill exhibited excellent bump interconnection reliability. It is well-understood that underfill materials can redistribute the stresses and hence enhance the reliability. Overall, both electrical and reliability tests demonstrated the feasibility of using RO3210 as microwave packaging substrate up to U-band applications.