The Comparative Study to Enhance Board Level Reliability Performance of Wafer Level Package At 0.25 mm Pitch Using Micro-Ball Drop and Electroplated Solder Technology
In this study, the board level reliability of WLP at 0.25mm pitch has been evaluated by employing board level reliability test following JEDEC include thermal cycling, drop shock and cyclic 4-point bend tests to verify the performance of shrunk bump size. The WLP test vehicle has been designed with 4-layer stack up structure, 4.0 × 4.0 mm die size and 15 × 15 ball array. The shrunk bumps of test vehicles were formed by using micro-ball drop and electroplated lead free solder bumping process after UBM plating completed. The shrunk bump size in WLP at 0.25mm ball pitch will enhance the risk of board level solder joint fatigue due to lower standoff height and smaller diameter of solder joint (higher bump stress concentration). In this work, we also evaluated different 4-layer WLP stack up structures for key design parameters including polyimide, RDL and UBM layers to reduce solder joint stress and thus enhance BLR performance All the study legs passed drop test with the 1st fail >100 drops and passed 200K times cyclic bend test without any failure. The TCT performance of micro-ball drop bumped legs showed better results with 1st fail passed 500X cycles. The drop, bend test and TCT performance are improved by new bump stack-up designs.
Enhanced Design and Reliability Analysis of Copper Post Wafer Level Package
In this study, the board level reliability (BLR) performance of different copper (Cu) post wafer level package (WLP) structures without epoxy or molding encapsulation have been evaluated and compared to standard WLP. The Cu post WLP test vehicle has been performed on different stack up structures of 4.7 x 7.1 mm2 package size at 0.4 mm ball pitch. The Cu post bumps of test vehicles were manufactured through main-stream production technologies including standard ball drop and electro-plated lead free solder after Cu post completed. The Cu post WLP will enhance the risk of board level solder joint fatigue due to thick Cu post without encapsulation will increase bump site stress. The optimized design parameters of package stack up with low temperature cured polyimide are implemented to accommodate the increased stress. In this work, we also evaluated a novel Cu post WLP stack up structure for fast package cycle time and fine pitch application. The improved BLR performance of large die size Cu post WLP is demonstrated in this investigation. The failure modes analysis and Weibull failure statistics are presented for the BLR results and recommendations as to the preferred Cu post WLP structure are also included.
Palm oil shell aggregate for lightweight concrete
Publisher Summary Increased agricultural production and the development of agro-based industries in many countries of the world have brought about the production of large quantities of agricultural wastes, most of which are not adequately managed and utilized. Low-cost building materials can be produced using inexpensive indigenous raw materials. Agricultural wastes that are renewable and are found in abundance in many countries present an interesting alternative to the traditional and sometimes imported building materials, particularly for low-cost construction. The use of agricultural wastes as aggregates in lightweight concrete can provides an alternative to conventional methods for the production of lightweight concrete. Lightweight concrete results in a reduction in the overall deadweight of a structure and provides a significant saving in the overall cost of construction. The use of less expensive alternative lightweight aggregates in the production of the concrete can provide further reductions in expense. The material properties and structural performance of lightweight concrete with palm oil shells as aggregates are similar to lightweight concrete produced using the more common lightweight aggregates such as clinker, foamed slag, and expanded clay. The palm oil shells are hard and are received as crushed pieces because of the process used to release the oil. Manual sieving is necessary to remove the large amount of fine particles. The shells are then air-dried before use. Because the palm oil shells are lighter than the cement matrix, the shells tend to segregate in wet concrete mixes. On the other hand, dry mixes using palm oil shells are relatively more difficult to work with when compared to ordinary concrete. Trial mixes are necessary to achieve a good mix design.