Masanobu Kohara

Thermal Stress-Free Package for Flip-Chip Devices

The purpose is to investigate the origin of technical progress as a result of the entropy law, to find its limitations, and to discover its best use.

Mechanism of electro-migration in ceramic package induced by chip-coating polyimide

The mechanism of electromigration between the inner leads in a ceramic package was investigated. The short-circuit failure between the neighboring pins of the ceramic package, in which a polyimide-coated LSI chip was assembled, was observed in tests after burn in. An analysis of the bypass which caused the failure found that the composition of the bypass was electromigrated nickel from the inner lead. Gas analysis showed that N-methyl-pyrrolidone (NMP) and water were included in the package. From these analyses, it was found that the progress of the migration was as follows: (1) NMP and water were evaporated from polyimide film during burn in if the polyimide was insufficiently baked; (2) NMP condensed on the inner leads and absorbed water during cooling to room temperature; and (3) the electromigration occurred between the inner leads with electric potential. This failure was eliminated by sufficiently baking the polyimide coating.<<ETX>>

Mechanism of electromigration in ceramic packages induced by chip-coating polyimide

The mechanism of electromigration between the inner leads of large-scale integrated (LSI) chips in ceramic packages that are coated by thick polyimides to prevent alpha-particle-induced soft errors is discussed. Short-circuit failures between neighboring inner leads in the packages were monitored in the final test after burn-in of LSI devices. The shorting paths between the leads were observed by an optical microscope and scanning electron microscope (SEM). It was found that the path was produced by a deposit between the inner leads. The deposit was found to be composed of electromigration nickel from the inner lead. Also, n-methyl-pyrrolidone (NMP) and water were found in the package by gas analysis. A possible short-circuiting mechanism is discussed. >

New developed of thin plastic package with high terminal counts

A small and thin quad flat package (QFP)-type plastic package for large-scale integrated (LSI) logic devices with high pin counts has been developed. The size of the package with 252 input and output pins is 17.3 mm by 17.3 mm, and the thickness is 1.52 mm. The pitch and the width of the leads are 0.25 and 0.1 mm, respectively. The main technologies for assembly of the package are tape automated bonding (TAB) interconnection technology, which has been developed for bonding of high-terminal-count LSIs, and the molding technology, which has also been developed for very small and thin plastic packages. The reliability of the package and the outer lead bonding of the package were evaluated, and it was confirmed that both the package and the bonding have no problem in the pressure cooker test (PCT), the temperature cycle test, and the high-temperature-storage test. >

A novel manufacturing technology of buried RuO/sub 2/-based thick film resistors in copper-polyimide substrate

A novel manufacturing technology of buried RuO/sub 2/-based thick-film resistor (TFR) in copper-polyimide system has been studied. Since electrodes of copper thin film are formed on the TFR by using photolithography and a plating method and the resistance of TFR has a widely linear relation, the resistance is determined only by the geometry of the TFR within 10% variation to the designed value. A specially optimized pulse laser irradiates the TFR through the polyimide film in order to accurately adjust the resistance without any degradation of the overcoating polyimide film on the TFR. The surface of the TFR is modified, and the resistance decreases with the shot number of the laser. Analysis by heat conduction theory suggests that the non-degradation of the polyimide film is based on the shortness of the laser pulse duration. Results of reliability tests show the stability of the resistance of laser-modified buried TFR.<<ETX>>

Resistance adjustment with short-pulse Nd:YAG laser for RuO/sub 2/-based thick-film resistors buries in polyimide film

To adjust the resistance of thick-film resistors (TFRs) buried in polyimide film, a process using a laser is proposed. Short-duration pulses from an Nd:YAG laser are used to irradiate the TFRs through the polyimide film. The TFR surface is modified thermochemically, and the resistance is reduced by an increasing amount with an increasing number of laser pulses. Because a 5-ns laser pulse is too short to start vaporization, no degradation of the polyimide film occurs. Temperature dependences of resistance show that the electrical conduction in the laser-modified TFR differs from that in the original TFR, because of higher electron density. >

A Study Of The Interface Between Polyimide And Plated Copper

A polyimide (PI) surface is analyzed by XPS at each electroless-copper-plating step. Zn ions are adsorbed on the PI surface, and subsequently replaced with Pd ions. Cu is deposited on the PI surface catalyzed by these Pd ions, As the surface concentration of Pd ions increases, the adhesive strength of the plated Cu to the PI surface increases. In the case of PI fabrication onto a plated Cu, no significant PI degradation is observed.