Method for the removal of surface oxides by electron attachment

An oxide, base electrode technology, applied in circuits, furnace types, printed circuits, etc., to solve problems that hinder accurate processing, control surface charges, change electric fields, etc.

Inactive Publication Date: 2011-05-04
AIR PROD & CHEM INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, this insulating shield traps surface charges that can alter the electric field and prevent precise process control
The method described is for melting the substrate metal surface only

Method used

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  • Method for the removal of surface oxides by electron attachment
  • Method for the removal of surface oxides by electron attachment
  • Method for the removal of surface oxides by electron attachment

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0109] The first experiment was performed using a laboratory scale furnace. The sample used was a flux-free tin-lead solder preform (melting point 183°C) on a grounded copper plate (anode), which was loaded into a furnace and heated at 5% H 2 N 2 heated to 250°C under airflow. When the sample temperature is in equilibrium, a DC voltage is applied between the negative electrode (cathode) and the grounded sample (anode) and gradually increased to about -2kV with a current of 0.3mA. The distance between the two electrodes is about 1 cm. Pressure is ambient atmospheric pressure. It was found that the solder wetted very well indeed on the copper surface. Good wetting of the fluxless solder on the copper surface can never be obtained at such low temperatures without an applied voltage, even in pure H 2 The same is true in , because with pure H 2 The effective temperature for removing tin oxide on tin-based solder is higher than 350°C. Therefore, this result confirms that the ...

Embodiment 2

[0111] Electron attachment assisted hydrogen fluxless soldering of several cathode materials was investigated with the same setup as in Example 1 by using the field emission mechanism. The results of the study are given in Table I.

[0112] As shown in Table I, the best results were obtained using a Ni / Cr cathode: it provided the highest melting efficiency and thus the shortest wetting time. It is believed that the Ni / Cr cathode produces a relatively large amount of electrons and has a suitable electron energy level compared to other cathode materials.

[0113] Table I: 250°C and 20%H 2 Effect of lower cathode material on wetting time

[0114] Cathode rod (1 / 16" diameter) material with tip

[0115] Nichrome

Embodiment 3

[0117] This example was carried out to investigate the efficiency of electron generation by the thermal-field emission method. A graphite rod with a diameter of 3 mm and a machined tip protruding from its surface with a length of several 1 mm was used as the cathode, the geometry of which was similar to Figure 2i shown in . Each protruding machined tip has a tip cone angle of 25 degrees. The graphite rod was heated by resistance using an AC power supply at 5% H 2 and 95%N 2 The gas mixture is heated to about 400 to 500°C. A DC voltage power supply of 5 kV was applied between a graphite cathode with a gap of 1.5 cm therebetween and a copper plate used as an anode. All tips on the graphite rod illuminate, indicating that electrons can be generated uniformly from the tips distributed on the graphite rod. Without heating the graphite rod, no electrons are emitted from the cathode or arc between one of the tips and the anode plate. This suggests that the combination of using...

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Abstract

Described herein are a method and an apparatus for removing metal oxides and / or forming solder joints on at least a portion of a substrate surface within a target area. In one particular embodiment, the method and apparatus to reduce metal oxides and form a solder joint within a substrate comprising a layer having a plurality of solder bumps by providing one or more energizing electrodes and exposing at least a portion of the layer and solder bumps to the energizing electrode.

Description

Background of the invention [0001] A method for removing metal oxides from the surface of substrates, including insulating substrates, is described herein. Also described herein is an apparatus for removing metal oxides from a substrate surface. [0002] Wafer bumping is a method of making thick metal bumps on chip bond pads for internal lead bonding. The bumps are usually made by depositing solder on the pads and then reflowing (referred to here as the first reflow) to alloy and change the shape of the solder bumps from a mushroom shape to a hemispherical shape. Chips with primary reflowed bumps are "flipped" to conform to the footprint of the solder-wettable end on the substrate, and then reflowed a second time to form solder joints. These joints are referred to herein as internal lead solder joints High melting point solder (e.g. >300°C) is usually used in the wafer bumping process because it allows subsequent assembly steps such as external lead soldering to continue ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H01L21/02H01L21/60
CPCB23K1/008B23K1/206B23K35/262B23K35/38C21D9/50C23G5/00H01L21/02068H01L21/4864H01L21/67069H01L24/16H01L2224/16H01L2924/0102H01L2924/01077H01L2924/01078H01L2924/09701H01L2924/14H01L2924/3025H05K3/3457H05K3/3489H05K2203/087H05K2203/105H01L2924/01087H01L2924/01322H01L2924/12042B23K2101/40H01L2924/00
Inventor 董春R·高希G·K·阿斯拉尼安
Owner AIR PROD & CHEM INC
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