Richard Hsiao

Enhancement of flip-chip fatigue life by encapsulation

Encapsulation of controlled collapse chip connection (C4) joints, using a filled epoxy resin with a matched coefficient of thermal expansion (CTE), has provided a substantial increase in the life of C4 joints in accelerated thermal cycle (ATC) fatigue testing on both low CTE organic and ceramic chip carriers. The C4 joints are encapsulated by dispensing a bead of the resin along an edge of the chip. The encapsulant flows underneath the chip by capillary action and completely fills the gap between the chip and the substrate. Optimization of the filler size distribution and resin rheology to obtain consistent flow under the chip without any bubbles is discussed. The filler size distribution and flow under the chip are shown in cross sections of several different materials, including low alpha emitting encapsulants for memory applications. Encapsulant formulations are tested by videotaping the flow of encapsulant under transparent quartz chips. The formation of bubbles as the encapsulant flows around the C4 joints and irregularities in the surface of the substrate can clearly be seen. Proper C4 encapsulation provides virtually complete coverage around all C4 connections. C4 life testing over various temperature ranges shows a five to ten times improvement for both memory and logic footprints when the C4 joints are encapsulated. The vast improvement in C4 joint reliability provided by encapsulation allows the C4 technology to be extended to much larger chips or to higher service temperature ranges without conventional distance from neutral point (DNP) constraints. >

Flip-chip solder bump fatigue life enhanced by polymer encapsulation

Encapsulation of controlled collapse chip connection (C4) joints, using a filled epoxy resin having a matched coefficient of thermal expansion (CTE), has provided a substantial increase in the life of C4 joints in accelerated thermal cycle (ATC) fatigue testing on both low-CTE organic and ceramic chip carriers. The C4 joints are encapsulated by dispensing a bead of resin along an edge of the chip. The encapsulation flows underneath the chip by capillary action and completely fills the gap between the chip and the substrate. Optimization of the filler size distribution and resin rheology to get consistent flow under the chip without any bubbles is discussed. The filler size distribution and flow under the chip are shown to cross sections of several different materials including low-alpha-emitting encapsulants for memory applications. Novel encapsulant formulations were tested by videotaping the flow of encapsulant under transparent quartz chips. The formation of bubbles as the encapsulant flows around the C4 joints and irregularities in the surface of the substrate can clearly be seen. Proper C4 encapsulation provides virtually complete coverage around all C4 connections. C4 life testing over various temperature ranges show a 5 to 10 times improvement for both memory and logic footprints when the C4 joints are encapsulated. The vast improvement in C4-joint reliability provided by encapsulation allows the C4 technology to be extended to much larger chips or to higher service-temperature ranges without conventional DNP (distance from neural point) constraints.<<ETX>>

Titanium carbide etching in high density plasma

Abstract Titanium carbide etching in fluorine-containing (CF 4 , CHF 3 , and SF 6 ) high density plasmas was investigated. The dependence of etch rates on gas composition and bias power was studied using the response surface method and the effects of source power and pressure were also examined. Argon was found to enhance the etch rate but the effect diminished when etching was controlled by the availability of the reactive species. The increase of the etch rate with increasing pressure indicated that the reactive radicals are the main etching species. The etch rate in SF 6 plasma was found to be up to four times faster than in CF 4 plasma because of the abundance of the active fluorine species. Electron spectroscopy for chemical analysis (ESCA) detected a carbon-rich surface layer for samples etched with CF 4 , CHF 3 and even a non-polymerizing SF 6 plasma.The results suggested that titanium was extracted preferentially from TiC during reactive ion etching in fluorinated plasmas.

Plasma-induced surface segregation and oxidation in nickel–iron thin films

Abstract Plasma-induced surface segregation and oxidation of Fe in nickel–iron (NiFe) thin films have been investigated. Reactive species in an oxygen plasma are found to be the driving force for Fe surface segregation and oxidation. Mapping of the film optical density change as a function of plasma exposure conditions indicates that segregation and oxidation are accelerated dramatically by the presence of reactive radicals and ion bombardment. For plasma oxidation protection, tantalum is found to be a more effective capping layer than tantalum oxide. With a tantalum capping layer, NiFe films maintain their magnetic properties until the tantalum capping layer is completely oxidized.

Tantalum plasma etching with minimum effect on underlying nickel-iron thin film

Abstract Removing tantalum (Ta) from nickel-iron (NiFe) surface in CF4/O2 plasma was first demonstrated to be a more robust process than argon ion milling in preserving and controlling the NiFe magnetic thickness during Ta overetch. A factorial study showed that the NiFe magnetic thickness loss could be further reduced by replacing CF4 with CHF3 and reducing O2 flow. For an optimized CHF3/CF4 process, the NiFe magnetic thickness loss for a 100-A Ta overetch was only 5 A. Electron spectroscopy for chemical analysis showed the presence of the fluorocarbon on the CF4/CHF3 etched Ta surface and nickel fluoride on the NiFe surface after Ta overetch. A mechanism of removing tantalum with minimum effect on the underlying nickel-iron thin film was also proposed.