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Printed circuit board with integral strain gageRelated Patent Categories: Registers, Coded Record Sensors, Particular Sensor Structure, MagneticPrinted circuit board with integral strain gage description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060231622, Printed circuit board with integral strain gage. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a Divisional Application of U.S. application Ser. No. 11/063,318 filed Feb. 22, 2005, which application is hereby incorporated by reference in its entirety. BACKGROUND OF THE INVENTION [0002] The present invention relates to a printed circuit board with an integral strain gage. Although the present invention addresses numerous problems, specific problems related to the manufacturing of printed circuit boards are discussed herein to provide a background of the invention. [0003] During printed circuit board manufacturing, it is advantageous to measure strain associated with a printed circuit boards. Strain measurements can be used for stress analysis purposes. During the manufacturing processes printed circuit boards undergo a variety of operations that can be stressful. For example populating a board during one manufacturing operation may cause damage to connections made in a previous manufacturing operation. Locating and monitoring areas where strain is being produced on a printed circuit board is desirable. Knowledge regarding strain can be used to assess electronic component failure modes within a printed circuit board to thereby alter or improve the manufacturing process as necessary to reduce or eliminate defects and/or otherwise improve quality. [0004] This problem has been addressed in the prior art by using conventional discrete strain gages attached to the surface of the printed circuit board with separate signal lead wires attached to the strain gage. In such an approach discrete strain gage sensors are glued to the top surface of the printed circuit board and attached to electrical circuitry via leadwires attached to the sensors. [0005] In the case of prior art strain gages, there is a significant installation cost associated with placing a strain gage on a printed circuit board. This step is performed by a technician which is time-consuming and costly. This type of labor intensive installation process is not consistent with the goals of an automated assembly process or a high volume PCB manufacturing environment. Moreover, because an automated process is not used the results obtained from strain gages installed in this manner may not be as accurate or useful as desired due to inconsistencies between installations. [0006] An alternative prior art approach has been to use strain-sensitive material applied by metal deposition directly to the board. This approach has allowed some use of printed circuit board manufacturing techniques, however there are significant disadvantages. In particular deposited metal does not provide the requisite strain-sensitive properties that may be required in more sensitive applications. Also, although printed circuit board manufacturing techniques are used, the use of a metal deposition step for the strain gage is a significant addition to the manufacturing process that may be cost prohibitive in particular applications. [0007] A further problem is that with the prior art approaches there are numerous limitations as to where strain can be measured. Strain sensors can not be located in positions which are not readily accessible. Every place where it may be advantageous or appropriate to measure strain is simply not accessible with a discrete sensor. [0008] Thus, despite these varying approaches used in the prior art, problems remain. Therefore, it is a primary object, feature or advantage of the present invention to improve upon the state of the art. [0009] Another object, feature, or advantage of the present invention is to provide for accurately and efficiently locating areas of stress in a printed circuit board. [0010] It is a further object, feature or advantage of the present invention to provide a printed circuit board with an integral strain gage as opposed to a discrete strain gage. [0011] It is a still further object, feature or advantage of the present invention is to provide an integral strain gage that does not require deposition of material directly on the printed circuit board. [0012] Another object, feature or advantage of the present invention is to provide an integral strain gage that is compatible with a multi-layer printed circuit board. [0013] Yet another object, feature or advantage of the present invention is to provide an integral strain gage for use in a printed circuit board that allows for flexibility with respect to where in the printed circuit board the strain gage is placed. [0014] A further object, feature or advantage of the present invention is to provide an integral strain gage that does not require using discrete sensors attached to the top surface of the printed circuit board. [0015] A still further object, feature, or advantage of the present invention is to provide an integral strain gage in a printed circuit board suitable for transducer purposes such as measuring deflection or force. [0016] Another object, feature, or advantage of the present invention is to provide an integral strain gage in a printed circuit board that is accurate. [0017] One or more of these and/or other objects, features, or advantages of the present invention will become apparent from the specification and claims that follow. SUMMARY OF THE INVENTION [0018] According to one aspect of the present invention a strain measurement layer for use in assembling a printed circuit board to provide for strain measurement on the printed circuit board is provided. The strain measurement layer includes an insulating layer having a top surface and a bottom surface. There is a strain sensitive layer of metallic foil adhered to the top surface of the insulating layer for measuring strain associated with the printed circuit board. There is a copper coating disposed on the strain-sensitive layer of metallic foil. The layer may also include a second strain sensitive layer on the bottom surface of the insulating layer and a second copper coating on the second strain sensitive layer. The strain sensitive layer may be patterned to provide one or more strain gage features. The copper coating may be patterned to provide for circuit features. [0019] According to another aspect of the invention, a printed circuit board includes a plurality of layers where at least one of the layers is a strain measurement layer adapted to provide for strain measurement of the printed circuit board. The strain measurement layer includes an insulating layer having a top surface and a bottom surface, a strain sensitive layer of metallic foil adhered to the top surface of the insulating layer for measuring strain associated with the printed circuit board and a copper coating disposed on the strain sensitive layer of metallic foil. The strain sensitive layer may be an outer layer or an inner layer. Also more than one strain sensitive layer can be used. Both the strain sensitive layer may be patterned to form various strain gage features. Similarly, the copper coating may be patterned to provide various circuit features. [0020] According to another aspect of the invention, a method for strain measurement on a printed circuit board is provided. The method includes providing a printed circuit board having a plurality of layers where at least one of the layers is a strain measurement layer having an insulating layer and a strain sensitive metallic foil adhered to the insulating layer for measuring strain associated with the printed circuit board. According to the method, strain is associated with the strain sensitive metallic foil as measured. The method allows for locating an area of high stress based on the strain. For example, the method provides for locating an area of high stress associated with solder connection failure in the printed circuit board. The resulting strain measurements can be used to provide information necessary to appropriately modify manufacturing process based on location of the areas of high stress. BRIEF DESCRIPTION OF THE DRAWINGS Continue reading about Printed circuit board with integral strain gage... 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