Low-k dielectrics materials in the active layers on the chip surface has become a hot topic as most 90nm devices and all 65nm devices utilize low-k dielectrics materials. Low-k dielectrics materials provide a significant increase in performance of the devices but lowk materials have very low mechanical strength compared to the traditional dielectric films due to their porous nature, which results in low strength and poor adhesion qualities of the low-k dielectric materials. These lead to a unique set of mechanical issues when lowk die are packaged, the reliability of low-k flip chip packaging has become a critical issue. The coefficient of thermal expansion (CTE) mismatch between the silicon die and the substrate produces a bending or curvature of the assembly upon changes of temperature. This type of thermal/mechanical stress can lead to solder bump fatigue, delamination of the low-k dielectrics materials and the failure of the electronic package. Due to the mechanical sensitivity of the low-k material, stresses induced by the package has been demonstrated to exasperate the problem. Additionally, the tight bump pitch and low standoff height of future packages reduce the flow performance of conventional liquid capillary underfill (CUF) that results in low productivity (low unit per hour (UPH)) and low throughput. Thence, there is a need to use better technology to improve these problems, new molding underfill flip chip ball grid arrays (terminator FCBGA ® ) structure is developed. It uses hydrodynamic pressure of a mold press to transfer molten molding underfill material into the flip chip undergap, Therefore it does not have the same limitation as the conventional liquid capillary underfill (CUF) and the biggest advantage is its better coplanarity, high throughput , low stress , stronger bump protection, better solder joint capability and same thermal performance, especially for large package size and large die size. New molding underfill structure terminator FCBGA ® can provide strong bump protection and reach high reliability performance due to epoxy molding compound (EMC) low coefficient of thermal expansion (CTE) and high modulus. This kind of structure can also be applied all kind of bump composition such as tin-lead, high lead, and lead free. Furthermore, this paper also describes the process and reliability validation result.

In this paper, new molding underfill structure is proposed. It shows many advantages, including a) Good package coplanarity b) Lower bump stress c) Lower 2'nd level ball stress d) Provide no limitation component design. Mold compound can hold big die and substrate together to keep good package coplanarity and give a uniform interface condition within big die area. Droping in heat spreader design gives the largest flexibility of die size and passive component size/number. Mold compound properties can be tailored to meet solder bump and low-K requirements. In addition, mold compound properties have high potential to meet Pb-free solder bump and low-K requirements. A high reliability, high thermal performance, and low package stress molding flip chip ball grid arrays structure is named terminator FCBGAR. It has many benefits, like better coplanarity, high through put (multi pcs per shut in molding process), low bump stress, and high thermal performance. In conventional flip chip structure, underfill dispenses and cure processes are a bottleneck due to low through put (dispensing unit by unit). For the high performance demand(high pin counts are necessary), large package/die size with more integrated functions needs to meet reliability criteria. Low k dielectric material, lead free bump especially and the package coplanarity are also challenges for package development. Besides, thermal performance is also a key concern with high power device. Low-k has become a hot topic as most 90nm devices and all 65nm devices utilize low-k dielectric. But low-k materials have very low mechanical strength compared to the traditional dielectric films due to their porous nature, which results in lower cohesive strength. Additionally, the tight bump pitch and low standoff height of future packages reduce the flow performance of conventional liquid capillary underfill (CUF) that results in low productivity (low unit per hour (UPH)) and low throughput. From simulation and reliability data, this new structure can provide strong bump protection and reach high reliability performance and can be applied for low-K chip and all kind of bump composition such as tin-lead, high lead, and lead free.

A high reliability and high thermal performance molding flip chip ball grid arrays structure which was improved from Terminator FCBGA®. (The structure are shown as Fig. 1) It has many advantages, like better coplanarity, high through put (multi pes for each shut of molding process), low stress, and high thermal performance. In conventional flip chip structure, underfill dispenses and cure processes are a bottleneck due to low through put (dispensing unit by unit). For the high performance demand, large package/die size with more integrated functions needs to meet reliability criteria. Low k dielectric material, lead free bump especially and the package coplanarity are also challenges for package development. Besides, thermal performance is also a key concern with high power device. From simulation and reliability data, this new structure can provide strong bump protection and reach high reliability performance and can be applied for low-K chip and all kind of bump composition such as tin-lead, high lead, and lead free. Comparing to original Terminator FCBGA®, this structure has better thermal performance because the thermal adhesive was added between die and heat spreader instead of epoxy molding compound (EMC). The thermal adhesive has much better thermal conductivity than EMC. Furthermore, this paper also describes the process and reliability validation result.

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The most important factor associated with cracking phenomenon during reflow soldering and molding are delamination at the interface of component material of packages. Copper has been widely used as substrate and leadframe as it has good thermal performance. However, Copper swface exposed to environment leading to weak interface bond with polymeric adhesive and encapsulant. Black oxide is a conversion coating applied onto the copper to improve its interfacial adhesion with polymeric adhesives. In this paper we will optimize the parameter of black oxide processing and apply it to flat heat spreader. The experiment results showed that the interfacial-bond strengths between the blackoxide-coated copper heat spreader and epoxy-based molding compound were measured in book mold shear tests.