Experience has shown that in thin packages ( 2 0~2 0~1 . 4 mm), molding defects occur somewhat more frequently with large devices (12.7x12.7 mm), and devices molded in the die-down configuration. For these unique conditions, the mold compound flow front advanced slowly over the top surface of the die and rapidly over the back of the die exposed by the X-flag l e a d m e design. The most frequent defect observed in evaluations of die-up and diedown molding was exposed silicon after molding, caused by the uneven mold compound flow.To develop a robust molding process window, designed experiments were used to evaluate leadframe downset, mold gate design, molding compound, and molding parameters. Results showed that the leadframe downset was the most significant variable to improve moldability, and a deeper downset produced the best results. The molding process was optimized with two molding compounds, and the manufacturing process window is robust over a large variety of device sizes in both die-up and die-down molding configurations. All

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Delamination of mold compounds under thermal stress conditions such as Air-to-Air Temperature Cycling (AATC) (−55°C −125° C) was studied for two passivation surfaces; SiN and SiON using C-Mode Scanning Acoustic Microscope (CSAM) and electrical testing for different intervals up to 2000 cycles. Both passivation surfaces were treated with oxygen-argon plasma prior to the molding process. It is found that SiN surface performed better than SiON electrically and without showing any delamination for the mold compound studied. Both passivation surfaces were analyzed for various surface groups by TOF-SIMS analysis immediately before and after the pre-mold plasma treatment process. Different surface groups such as CH, NH etc. were identified, but the major difference was found in the OH intensity. Fraction of OH is significantly increased after plasma treatment for SiN surface while it is decreased for SiON surface. It is inferred that OH group can play a role in enhancing the mold compoundpassivation adhesion and hence provide better delamiantion resistance.