Bob H. Lee

Sub-band adaptive IIR noise cancellation

A subband adaptive infinite impulse response (IIR) noise cancellation scheme whose structure enables the cancellation of multiple sinusoidal interferences in a received speech signal is presented. Compared with the classical least mean square adaptive noise cancellation method, this new structure has two major differences. First, the quadrature mirror filter technique is used to decompose signals into subbands. Second, a new constrained adaptive IIR notch filter and adaptive IIR bandpass filter are developed to form an adaptive IIR noise canceller and used to remove the multiple-frequency, or harmonic, noise from a received speech signal. Computer simulations were done using a set of actual speech signals corrupted by car engine noise. Experiments demonstrate that more than 20-dB signal-to-noise ratio improvements can be achieved.<<ETX>>

Package structure interaction induced molding issues in MCM packages

As we move forward to newer silicon technologies that requiring MCM dual pad leadframe design and packaging solutions with tighter process margins, it is becoming imperative to resolve ppm wire sweep failure which is critical in transfer molding process as excessive results in shorting of wires, current leakage and electrical failure. Wire sweep has been proved to be closely related to bond span, wire length, height, mold flow direction, mold gate design...etc. With the MCM dual pad leadframe design, architecture dependent mold flow phenomena and race track profile are observed and impact on wire sweep failure rate. Although the impact could be positive on wire sweep, it is considered not acceptable as it would restrict the package design and could introduce incomplete filled or void issues. Besides, it could not meet todays zero ppm mindset in the automotive and critical applications industry.The deep dive study on mold process and mold compound is carried out. Firstly, key molding parameters were identified, namely transfer speed, clamp pressure and transfer pressure point. Wire sweep locations, wire sweep distribution were used as the output parameter to identify the mold process window. Furthermore, the effects of mold compound material properties were also investigated. The results suggest mold compound properties play a critical role in resolving random wire sweep for the MCM dual pad packages. This paper documents all the studies, evaluations and verification runs done on multi package structures, optimized mold process and mold compound properties to establish a robust package solution for MCM packages.

Inter-connecting process investigation to resolve delamination

Delamination on the interface between mold compound to die, die paddle and inner leads study has been on-going for quite some time. This is a chronicle defect which will result in electrical continuity failure if delamination penetrates into the interface of mold compound to die surface and mold compound to inner leads e.g., delamination on inner leads or die surface to cause wire broken after thermal stress. To resolve delamination, better materials are needed such as Lead frame, die attach and mold compound. Other than that, a process optimization is also a must to achieve delamination free result. The paper portrays the phenomenon of how delamination occurred after improving the BOM e.g., less water absorption and higher adhesion mold compound. During qualification stage, no delamination occurred after thermal stress. But, on mass volume production run, the delamination occurs on inner leads by sampling check. Four “M” Men, Material, Method and Machines are thoroughly checked and compared with its qualification built and mass production run. No difference or conclusion can be observed and made. But, the delamination was there though no finding/difference was observed. However, one conclusion can be made is qualification is small volume but mass confirmation run is large volume. Based on the assumption, Delamination comparison between small volume VS. large volume was conducted to check the difference. Then, the root cause as die attach outgassing to cause contamination on package is observed. The contamination is later turn into delamination after Thermal.

Mold compound fracture mode study for high reliability package

This paper presents TI development of high reliability molding compound material for power enhancement packages with PPF LDF. The mold gate remains due to good molding compound high adhesion and low flexural strength/Modulus are observed in several packages during mass production run. Correlations of adhesion and modulus change with Respect to its fracture strength under different conditions are studied. As a result, the gate remains solved by achieving the sweet spot based on material properties on optimized molding parameters. The gate remains on LDF side rail which will be stuck at T&F process. A modification to dies and LDF design can jump across the hurdle, but high investment needed. With this study, the gate remains can be conquered after an effective DOE with the proper understanding of Material (Mold compound) properties and Mold Machines capability.