Chip Bonding

Fig. 5. Various layers in a flip-chip bond, where BLM = ball-limiting metallurgy and TSM = top-surface metallurgy (3).

The most widely used high melting point solder for flip-chip bonding is 95% lead—5% tin solder (mp C) eutectic 60% lead—40% tin solder... 

The adhesives are suitable for use in flip chip bonding of semiconductor parts. They exhibit good shelf stability, productivity, strength properties and heat resistance. The electrical properties, such as dielectric constant and dielectric loss tangent are highly satisfactory. 

For chips that are flip-chip bonded, additional conductor layers may be required to redistribute the I/Os from underneath the chip to the engi-... 

The most advanced implementation of cofired-ceramic-packaging technology is the thermal conduction module (TCM) used in large-scale computers (IBM) (4, 72, 74). This package can accommodate over 100 flip-chip-bonded ICs on a 90 by 90 mm cofired ceramic substrate. The multilayer ceramic substrate contains 33 metal layers for chip pad redistribution, signal interconnection, and power distribution (Figure 14). Each chip contains 120 bonding pads, and 1800 pins are brazed to the bottom of the substrate for connection to a PWB. 

Copper has been employed commonly in relation with carbohydrates and aminoacids but other analytes can also be determined. Microalignment of the electrode with the channel outlet [89], deposition of a thin layer [81,108] or incorporation of a wire [21] are examples of in-channel formats. End-channel configurations such as those obtained by using a guide tube [11] or attaching a Cu wire perpendicularly to the outlet [32] after chip bonding were tested. Carbon nanotube (CNT)/copper composite electrodes have proved to be more sensitive, compared to the Cu and CNT alone, in the determination of carbohydrates [109]. 

Reduction of background fluorescence can be achieved by using the fused silica substrate. In this way, the detection limit can be improved [106]. Further reduction in the background could be achieved by optimizing the chip bonding procedure... 

The photodiodes of the imagers presented in US-A-4566024 are formed in a p-type HgCdTe substrate by diffusing n-type impurities from two opposite faces, a front face and a rear free, of the substrate. The photodiodes can be connected to a read-out device by a flip-chip bonding process on the rear face of the substrate and still be illuminated from its front free. 

A process to manufacture an imager is disclosed in JP-A-63260171. Photodiodes, formed in HgCdTe chips, are tested before they are mounted on a temporary substrate. The chips are further treated before they are bonded to a CCD with a flip-chip bonding process. 

The invention of GB-A-2246662 refers to testing of an imager by the use of a test element group. Elements of the test element group are connected by indium bumps to connection pads on a read-out substrate in the same flip-chip bonding process which connects detector elements to the read-out substrate. 

The problem of cross-talk between adjacent photodiodes is solved in JP-A-2303160 by forming islands of HgCdTe, comprising photodiodes, on a CdTe substrate and then bonding them to a read-out device by a flip-chip bonding process. 

HgCdTe wells S, comprising photodiodes 7, are formed in a CdTe substrate 1. The anodes and cathodes of the photodiodes are connected by indium columns 12 and 13 to a silicon substrate 9 by a flip-chip bonding process. 

In US-A-4369458 the contact array of an infrared detector includes a substantially greater number of contacts than the contact array of a signal processor. At the flip-chip bonding operation it is not a prerequisite to precisely align the two integrated circuits in a one-to-one contact relationship. 

When a silicon read-out chip and an HgCdTe detector chip are bonded together by a flip-chip bonding process, the chips are exposed to a mechanical stress which may lead to damages, especially of the fragile detector chip. Photo-resist films are used in JP-A-61059771 (Fujitsu Ltd, Japan, 27.03.86) to form a spacer. The spacer reduces the mechancial stress of the semiconductor chips during the bonding process. 

An alternative approach is to form an hybrid array [20], The detector array is then formed in a mercury cadmium telluride substrate and the readout circuits are formed in a silicon substrate. The hybrid arrays are presented in part two. Detector arrays having detector elements which are provided with individual read-out leads formed in or on a non-active supporting substrate are presented in chapter 2.1. The detector elements may however be directly connected to a read-out chip which is bonded to the detector chip. A flip-chip bonding technique using indium bumps may be used as shown in figure 3 [21]. 

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