Spectra-Physics, Inc. v. Coherent, Inc.
| Decision Date | 17 August 1987 |
| Docket Number | INC,SPECTRA-PHYSIC,Nos. 86-1114,86-1133,s. 86-1114 |
| Parties | , Appellee/Cross-Appellant, v. COHERENT, INC., Appellant/Cross Appellee. Appeal |
| Court | U.S. Court of Appeals — Federal Circuit |
Karl A. Limbach, of Limbach, Limbach & Sutton, San Francisco, Cal., argued for appellant. Of counsel were J. William Wigert, Jr. and Michael A. Stallman, of Limbach, Limbach & Sutton, San Francisco, Cal.
James W. Geriak, of Lyon & Lyon, Los Angeles, Cal., argued for appellee. With him on the brief were John M. Benassi, James H. Shalek, David B. Ritchie and Paul H. Meier, of Lyon & Lyon, Los Angeles, Cal.
Before RICH, Circuit Judge, SKELTON, Senior Circuit Judge, and ARCHER, Circuit Judge.
These are cross-appeals from the December 16, 1985, judgment of the United States District Court for the Northern District of California holding both of Coherent's patents in suit, No. 4,378,600 entitled "Gas Laser" issued on March 29, 1983, to James L. Hobart (the Hobart patent) and No. 4,376,328 entitled "Method of Constructing Gaseous Laser" issued on March 15, 1983, to Wayne S. Mefferd (the Mefferd patent), invalid for lack of enabling disclosure under 35 U.S.C. Sec. 112, first paragraph, after originally entering judgment on a jury verdict finding claims 2, 5, 7, and 18 of the Hobart patent and claim 10 of the Mefferd patent valid and infringed by Spectra-Physics, Inc. (Spectra).
We reverse the district court's holding that both patents are invalid for lack of enablement. We also reverse, however, the court's finding that both patent specifications complied with the best mode requirement of Sec. 112, and thus affirm the judgment that the patents are invalid, but on a different legal ground.
Before discussing the legal aspects of this case, we first explain the technology involved which gave rise to them.
The Hobart patent is directed to an ion laser structure and the Mefferd patent to a method of fabricating an ion laser. "Laser" is an acronym for l ight a mplification by § timulated e mission of r adiation. 1 An ion laser is a type of gaseous laser. The lasing medium, typically argon or krypton gas, is contained within a sealed discharge tube which is axially aligned with a pair of mirrors to form the optical cavity or resonator.
For lasing to take place, the argon or krypton gas must be excited to elevated energy states. This is accomplished by providing a high-energy electrical discharge through the gas. The discharge through the laser must then be constrained to a straight line along the laser's optical path and pinched to a small diameter to concentrate its energy into a small elongated volume.
The discharge through the laser is extremely hot--up to 6000 degrees C. The exterior of the laser, however, must operate at room temperature, requiring dissipation of large amounts of heat by external cooling. It is also important that gas pressure be uniformly controlled along the discharge tube.
For some reason, not entirely agreed upon by physicists, the gas tends to move to one end of the tube or the other. This phenomenon, known as "pumping," causes an uneven gas pressure differential in the discharge tube, resulting in poor performance or no performance at all.
The Hobart patent is directed to a gas laser having an improved laser discharge tube. 2 The discharge path of the laser is determined by coaxially aligned apertures in a series of spaced-apart tungsten discs within the laser discharge tube. The discharge tube itself is a thin-walled ceramic tube, for example, of alumina (Al2 O3 ). Heat from the tungsten discs is transmitted by conduction to and through the ceramic tube (26), which is surrounded by a water jacket, by copper cups (50) attached to the inside of the tube. See Fig. 1 below, which is a dissected sectional view showing two end portions with a substantial portion of the central section omitted, the broken line representing the longitudinal axis.
Figure 1.
Cross-sectional View of Laser Structure Claim 1 calls for "means for providing a heat conduction path from the central aperture of each of said discs to and through the tube wall." This includes both means for attaching the tungsten discs (48) to the center opening of each copper cup and means for attaching the cups to the inside wall of the ceramic tube. High thermal conductivity is achieved by brazing or soldering which provides a permanent metallic contact between the cups and the tube wall.
The Hobart patent further discloses and claims a "shield" feature which is a cylindrical ring coaxially attached to or formed integrally with each of the copper cups. 3 These shields (56) aid in minimizing gas pumping within the discharge tube.
The Mefferd patent describes a method of fabricating the laser structure of the Hobart patent. 4 The problem addressed in
the Mefferd patent is how to insert and hold in place the heat conducting cups inside the long, slender tube, while at the same time maintaining the apertured discs in precise alignment. The patent discloses a "floating" disc technique whereby the disc apertures are aligned by tensioning a mandrel that has been passed through each of the disc apertures. Once the disc apertures are aligned, the whole assembly is brazed to permanently bond the parts within and to the tube walls. See Fig. 12 below in which the copper cups are 50, the shields 56, the discs 48, the mandrel 74 and the ceramic tube 26. The figure shows a partial assembly before the brazing of the discs to the cups, which is done in a vertical position with end "B" upward.
Figure 12.
Cross-sectional View Illustrating Assembly of Cups and Discs
Both the Hobart and Mefferd patents stress the importance of the bond between the copper cups and the ceramic tube. Poor thermal contact between them results in higher disc temperatures which in turn impedes the gas flow through the tube. For the laser to be reliable, the copper-ceramic bond must also be able to withstand repeated heat cycling. Due to the differing rates of thermal expansion of copper and alumina, the bond is subject to compressive forces as the laser heats up and tensile stress during cooling.
Dr. Hobart initially approached the problem of how to make the critical copper to ceramic bond by experimenting with soldering. These attempts were unsuccessful and no attempt was made to even try to solder together any laser shaped parts. Wayne Mefferd was then brought in to solve the attachment problem. His solution was brazing.
While the patent specifications disclose pulse soldering as one method of attachment, brazing is clearly the preferred method. In this process, a brazing shim 68, Fig. 4, is placed between the copper cup 50 and the inner wall of the ceramic tube 26, see Fig. 3, and the whole assembly is heated to the melting point of the braze material.
During heating the cup is mechanically expanded into contact with the tube by means of an expansion tool inserted into tube 26.
The patents further disclose "TiCuSil" as the preferred brazing material. This material is a copper silver eutectic (an alloy whose ingredients are proportioned to have the lowest possible melting point) with a small percentage of titanium added for making a ceramic to metal seal under what is known as the active metal process. In this process, the titanium invades and wets the ceramic so that the copper-silver braze material can hold the copper to the ceramic. In the absence of an active metal alloy component such as titanium, the ceramic must be premetalized with, for example, moly-manganese (MoMn), to provide a metallic surface to which the copper-silver braze material will adhere.
The TiCuSil active metal process is preferred because it requires only one step and avoids the need for premetalization. In addition, the copper cups cannot be electrically connected because this destroys the evenly graduated electrical potential down the bore of the tube which is required for the laser to operate. Thus, any premetalization must be in circular stripes along the inner surface of the tube so that each copper cup can be brazed or soldered to a different stripe.
According to the standard product specification sheet, TiCuSil should be brazed at 850 degrees C. The sheet also specifies that the braze should be performed in a vacuum or in a neutral atmosphere of dry argon gas. Using these general guidelines, Mefferd developed a six-stage braze cycle for using TiCuSil to attach the copper cups to the ceramic tube. "Braze cycle" is a term of art which refers to a process defined by specific parameters of temperature, length of times at given temperatures, atmosphere, and pressure.
Mefferd knew that there were tradeoffs in the braze cycle. For one, it is generally desirable to heat the parts as fast as possible. As the parts are heated, however, "outgassing" occurs and contaminants trapped in the parts are released into the atmosphere of the oven. The vacuum pump removes the outgassed contaminants, but if the outgassing is too rapid, then the pressure may rise and the pump will not work. Also, if oxygen is evolved as part of the out-gas, the titanium may react with it and degrade the strength of the braze joint.
In assessing the tradeoffs, Mefferd let the pressure control the braze cycle, as one experimental approach. For example, Mefferd held the pressure in the oven at 10-4 torr while the assembly was initially heated from 0 to 750 degrees C. This took from an hour and a half to two hours. In the next step, he held the temperature at 750 degrees for ten to fifteen minutes while further reducing the...
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