Patent Application
20140355179
This subject invention relates to portable electronic devices and housings therefore.
Modern portable electronic devices such as cellular telephones include a touch screen assembly behind a cover glass. See Published U.S. Application No. 2012/0281380 incorporated herein by this reference. One typical goal is to maximize the exposure of the cover glass (and the touch screen assembly) and to render the cover glass very thin (e.g., less than 3 mm thick).
According to the above referenced published patent application, adhesives are usually used to secure the cover glass to the housing. In the disclosure, the housing includes mounting brackets attached to housing side members. An adhesive is used to secure the cover glass to the mounting brackets.
When such a cellular telephone is dropped, the glass can easily crack and a crack at the periphery of the cover glass will propagate resulting in the cover glass shattering. Edge and corner cracking is common.
Using a softer, more pliant material for the cover glass is not possible due to the need for the cover glass to be resistant to scratching.
In U.S. Pat. No. 4,393,105, also incorporated herein by this reference, two panes of glass were secured to an aluminum spacer frame to form a thermal pane window using anodic bonding. But, the aluminum spacer frame material was chosen specifically to have a very low yield strength so high stresses were not induced in the glass panes.
In this invention, in contrast, it is desirable to induce stress into the cover glass to increase its tensile strength and to prevent both cracking and crack propagation.
Conveniently, the anodic bonding process which secures the cover glass to the portable electronic device housing portion (side member, mounting rail, or internal metal frame) itself may result in induced compressive stress within the cover glass and thus the process which serves to secure the cover glass to the housing portion without the need for an adhesive also strengthens the cover glass.
Featured is a method comprising applying a portable electronic device housing portion to a cover glass which has been heated to generate ionic conductivity therein, and anodic bonding the cover glass to the housing portion. In cooling the assembly, compressive stress is induced within the cover glass to increase its tensile strength. The method may further include the step attaching a touch screen assembly to the cover glass. In one version, the cover glass includes silica glass or is sapphire. Heating the cover glass may include heating the cover glass to a temperature of 350° C.+/−100° C. Heating may occur in an oven or via a hot plate.
The step of inducing compressive stress within the cover glass may include choosing a housing portion material which has a coefficient of thermal expansion substantially higher than the coefficient of thermal expansion of the cover glass. Preferably, the step of inducing compressive stress within the cover glass further includes choosing a housing portion material which does not have too low or too high a yield strength. In one example, the housing portion is made of aluminum.
Anodic bonding the cover glass to the housing may include placing a first electrode on the cover glass and a second electrode on the housing portion. In some examples, the housing portion is side member, a mounting rail, or a metal frame about the cover glass.
Also featured is a method comprising heating a glass portion to generate ionic conductivity therein and heating a housing portion to expand it to a greater extent than the glass portion. When the housing portion is so expanded, it is bonded to the glass portion at the periphery thereof using anodic bonding. The assembly is cooled and the housing portion contracts to a greater extent than the glass portion which induces compressive stress within the glass portion at the periphery thereof.
Also featured is a portable electronic device comprising a housing portion, a cover glass, and an electrostatic bond between the housing portion and the cover glass at the periphery of the cover glass. The housing portion induces compressive stress within the cover glass at its periphery increasing its tensile strength. The portable electronic device may further include a touch screen assembly secured to the cover glass.
The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. The references Bonding Properties of Metals Anodically Bonded to Glass, Briand, Weber, deRooij; Sensors and Actuators A: Physical 114 issues 2-3, 543-549, 2004; Anodic Bonding of Glass to Aluminum, Schjolberg-Henrikson, Poppe, Moe, Storas, Taklo, Wang, Jacobsen; Micorsyst Technol (2006) 12: 441-449 DOI 10.1007/s00542-005-0040-8; Interfacial Phenomena in Electric Field-Assisted Anodic Bonding of Kovar/Al Film-Glass, Chen, Gu, Dong, Trans. Nonferrous Met. Soc. China Vol. 11 No. 5, Oct. 2001; and Field Assisted Glass Sealing, Wallis; and Electrocomponent Science and Technology 1975, Vol. 2, No. 1 pp. 44-53 are all incorporated herein by this reference.
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer
In
Electrode 34b may be a plate shaped member or a frame shaped member. Alternatively, a probe with a small tip may be used. The probe may be static or may be maneuvered to contact different parts of the rails, for example.
In
Preferably, the metal housing component has a sufficiently high yield strength such that it induces compressive stress within the cover glass (e.g., silica glass or sapphire) to increase the tensile strength of the cover glass and to prevent cracking or at least to prevent crack propagation. In one example, the metal component is a metal or metal alloy such as aluminum, 304 and 316 stainless steel, nickel, titanium, and nickel chromium alloys (e.g., “Inconel”) could also be used. At the same time, the metal alloy should be configured (e.g., thin enough) and have a yield strength which is not too high so that the cover glass does not crack on cooling. Yield strengths ranging from 20-40 kpsi may suffice. In other examples, the housing is a multi-layered ceramic enclosure. See Published application No. US 2013/0078398 incorporated herein by this reference. If sapphire is used as the cover glass, oxygen may be ion implanted into the sapphire surface to provide excess oxygen atoms for anodic bonding to occur.
The housing component is preferably applied to the cover glass as depicted in the examples of
Heating can occur with the electrodes applied, in an oven, for example. The electrodes may be plate electrodes, probes, and/or circumferential “spacer electrodes” 34b shown in
A hermetic seal between the housing and the cover glass thus effected via anodic bonding. Thereafter, the voltage and heat are removed and the assembly is allowed to cool, step 80. Because the coefficient of thermal expansion of the aluminum housing (e.g., 22×10−6/° C.) is much higher than the typical coefficient of thermal expansion of the cover glass (e.g., 8×10−6/° C.), during the anodic bonding process and during cooling in step 80, the aluminum housing induces compressive stress within the cover glass and increases its tensile strength. Preferably, the housing frame and cover glass are heated separately, mated at the high temperature, anodic bonded, and then cooled.
In
In the manufacturing process, the touch screen assembly can then be applied to the cover glass as shown at step 82 in
The result is a process which hermetically seals the cover glass to the housing portion and at the same time strengthens at least the periphery of the cover glass.
In other examples, improvements are made in the cover glass/housing interface using anodic bonding techniques even without the heating and cooling steps described above. For example, the anodic bond at the interface between the glass and the housing functions to prevent the propagation of any cracks due to dropping the electronic device and the like. The heating and cooling steps described herein, if used in one preferred embodiment, promote the anodic process and may be varied based on the characteristics of the materials to be bonded. A number of other sequences of heating and applying the voltage are possible, as are variations in the preparation of the glass/and/or metal frame. Example includes turning on the voltage while the heating is ramping up and/or applying a thin film of metal to the edge of the cover substrate or to the metal frame to improve the anodic bonding.
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
Other embodiments will occur to those skilled in the art and are within the following claims.
