The patentee sued a number of defendants for infringement of its three patents. The district court severed the case against one defendant and stayed the litigation as to the remaining defendants. The severed litigation proceeded through summary judgment, where the district court found noninfringement on the basis that the alleged infringer only sold software, and the claims required both hardware and software. The district court also construed the asserted claims and held that, as a matter of law, the patentee failed to show that the “accused software met the relevant limitations of the claims as construed.”

The patentee appealed the district court’s summary judgment ruling. The Federal Circuit upheld the district court’s decision, without an opinion, pursuant to Federal Circuit Rule 36. Subsequently, in the proceedings against the other alleged infringers, the patentee stipulated that it could not prove infringement under the court’s claim construction. The district court entered its judgment accordingly, and the patentee appealed.

The alleged infringers asserted the mandate rule and collateral estoppel to prevent the patentee from appealing the claim construction order. The Federal Circuit held that its Rule 36 decision could have affirmed the district court’s grant of summary judgment on either of two independent bases. The mandate rule was inapplicable because the district court’s claim construction was not essential for the Federal Circuit to uphold the initial judgment of noninfringement. Collateral estoppel did not apply because the alleged infringers could not show that the district court’s claim construction was the reason for the loss. Thus, the Federal Circuit did review the district court’s claim construction de novo finding certain errors in the constructions of certain claim terms.

A copy of the opinion can be found here.