A U.S. appeals court has ruled that Rambus inappropriately destroyed documents related to patent cases it filed, but the judges asked a lower court to reassess its decision to toss out a lawsuit because of the document shredding.

Both memory chip makers Micron and Hynix Semiconductor Inc had accused Rambus of destroying documents relevant to the litigation.

Rambus shares were down 15 percent in early afternoon trading on Nasdaq on Friday.

It is undisputed that Rambus destroyed between 9,000 and 18,000 pounds of documents in 300 boxes, the appellate court said, adding the U.S. District Court in Delaware might still decide the lawsuit should be dismissed.

Micron had won in the Delaware court when a judge invalidated 12 patents, citing document destruction by Rambus as the reason.

But Rambus won against Hynix in a separate trial, when a federal judge in California found that nine Rambus patents were valid and had been infringed.

Hynix and Micron accused Rambus of holding improper shredding parties even as the company laid out plans to sue them for patent infringement.

Trading in Rambus was halted six times on Friday as the stock hit circuit breakers after rapidly rising and then falling through the 10 percent threshold in a matter of minutes.

At nearly 7 million shares, volume was over eight times the daily average.

(Reporting by Diane Bartz; Editing by Tim Dobbyn)