Glass manufacturing – Processes – Fusion bonding of glass to a formed part
Reexamination Certificate
1998-03-06
2004-11-30
Chin, Peter (Department: 1731)
Glass manufacturing
Processes
Fusion bonding of glass to a formed part
C156S272200, C156S273100, C156S273900, C156S274400, C205S114000, C205S124000
Reexamination Certificate
active
06823693
ABSTRACT:
BACKGROUND INFORMATION
The invention relates to anodic bonding.
One way a glass material may be bonded to an oxidizable material (e.g., a metal, such as silicon) or another glass material is through a process called anodic bonding. During anodic bonding, heat is applied to the materials to be bonded, and oxygen ions in the heated glass material are drawn across a junction (where the two materials contact each other) to form a chemically bonded oxide bridge between the two materials. To draw the oxygen ions across the junction, an electric field typically is applied to the materials to create a flow of charge through the materials. The materials are heated until the alkali and alkaline earth ions become mobile allowing non-bridging oxygen ions to also diffuse. In this manner, negatively charged oxygen ions flow in one direction across the junction, and positively charged ions (e.g., alkali ions, such as sodium and lithium) flow in the opposite direction across the junction.
Referring to
FIG. 1
, as an example, anodic bonding might be used to bond a glass substrate
10
to a metal, such as silicon
12
. To accomplish this, an electrode
14
is placed on the glass substrate
10
and biased (via a DC source
20
) at a negative potential relative to the potential of another electrode
16
that is placed on the silicon
12
. If the film of silicon is electrically conductive, electrical contact may be made directly to the film. In this manner, the two electrodes
14
and
16
establish an electric field across the glass substrate
10
and the silicon
12
.
This electric field causes the positive ions (e.g., sodium ions) of the substrate
10
to move toward the negative electrode
14
and oxygen ions of the substrate
10
to move toward the positive potential (e.g., either toward the positive electrode
16
or the film of silicon, if conductive). As a result, the oxygen ions diffuse across a junction
18
(where the two materials contact each other) into the silicon
12
and react as follows:
2O
−
+Si=>SiO
2
+2e
−
Thus, the oxygen ions react with the silicon to form silica (SiO
2
), a stable oxide, which bonds the glass substrate
10
and the silicon
12
together. The amount of silica that is formed depends on the amount of charge that is supplied by the source
20
.
Therefore, the rate at which the silica is formed depends on how fast charge is supplied by the source
20
, or stated differently, the rate at which the silica is formed is a function of the magnitude of a current (called I
BOND
) that is provided by the source
20
. Although the rate at which the anodic bond is formed depends on the magnitude of the I
BOND
current, the quality of the bond is also quite often a function of the I
BOND
current.
When the I
BOND
current has a large magnitude, the relatively slow flow rate of the glass substrate
10
causes the silica to be formed in a small area. Better bond quality is typically achieved when the I
BOND
current has a smaller magnitude which allows the silica to form over a much larger area.
Although a minimum amount of silica must be formed to ensure a good bond, too much silica formation may present difficulties. For example, the silicon
12
might be a thin layer that is formed on top of a substrate. As a result, forming too much silica may delaminate, or remove, the silicon layer from the substrate.
Although anodic bonding has traditionally been used to bond small materials (e.g., materials having no dimension greater than six inches) together, anodic bonding may be used to bond materials to a larger substrate. For example, anodic bonding might be used to attach glass spacer rods to oxidizable material of a face plate of a field emission display (FED). Because of the relatively large size (e.g., dimensions greater than 12 inches) of the face plate, temperature gradients cause the magnitudes of the I
BOND
currents to vary, depending on where the anodic bonding occurs on the face plate. As a result, even if the same potential is used to bond all sites on the face plate, the silica is formed at different rates among the different bond sites.
SUMMARY OF THE INVENTION
The invention is generally directed to anodically bonding two materials together by monitoring and controlling the amount of charge used to bond the materials.
The advantages of the invention may include one or more of the following. The amount of oxide used to bond the materials is precisely controlled, and this amount is not affected by temperature. Several pieces of one material can be bonded to another relatively large material at one time. The cost of manufacturing flat panel displays is reduced. The time required to manufacture flat panel displays is reduced. Better quality control is maintained over the anodic bonding.
Generally, in one aspect, the invention features a controller for use with an anodic bonding system that has a charge flowpath for supplying charge to bond materials together. The controller includes a switch and a circuit. The switch is configured to control a flow of the charge through the charge flowpath. The circuit is configured to monitor a rate of the flow, use the rate to determine an amount of the charge supplied for bonding, and based on the amount, operate the switch to control the flow.
Generally, in another aspect, the invention features a system for bonding two materials together at a junction between the materials. The system includes an energy source, electrodes in contact with the materials, and a controller. The controller is configured to connect the energy source to the electrodes to transfer charge from the energy source to the junction, and disconnect the energy source from the electrodes after a predetermined amount of the charge has been transferred to the materials.
Generally, in another aspect, the invention features a system for bonding a number of first materials to a second material near different regions of the second material. The system includes an energy source and electrodes that are configured to establish charge flowpaths. The system also has controllers. Each different controller is associated with a different one of the flowpaths and is configured to cause charge to flow from the energy source through the associated flowpath until a predetermined amount of the charge flows through the associated flowpath.
Generally, in another aspect, the invention features a system for bonding glass spacer rods to a face plate of a flat panel display. The system includes an energy source, electrodes and controllers. The electrodes are configured to establish charge flowpaths. Each different flowpath is associated with a junction located between a different one of the glass spacer rods and the face plate. Each different controller is associated with a different one of the flowpaths and is configured to allow charge to flow from the energy source through the associated flowpath until a predetermined amount of the charge flows to the junction associated with the flowpath.
Generally, in another aspect, the invention features a method for anodically bonding two materials together. The method includes placing the two materials in contact with each other to form a junction between the materials. A current is applied through the materials to transfer charge to the junction. This current is monitored to determine the amount of the charge being transferred to the junction. The current is controlled based on the amount.
Generally, in another aspect, the invention features a method for bonding a number of first materials to a second material at different regions of the second material. The method includes placing each of the first materials in contact with the second material to form junctions between the first and second materials. Currents are applied through the first and second materials to transfer charge to the junctions. The amounts of charge transferred to each of the junctions are monitored, and based on the amounts, the currents are selectively controlled.
Generally, in another aspect, the invention features a method for anodically
Hofmann James J.
Piper Glenn W.
Chin Peter
Micro)n Technology, Inc.
Trop Pruner & Hu P.C.
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