Taiwan's top IC substrate maker Unimicron is under a second round of searches by prosecutors over how it labels where its products are made — bad news for the company and a warning shot for the whole Taiwanese circuit-board industry.

• Investigators returned to Unimicron's Taoyuan plant and took away computer files and engineers, days after a first search.
• The case centres on possible false origin labelling, a criminal offence in Taiwan.
• Unimicron says the disputed goods are ordinary circuit boards, not its flagship substrates, and that it is cooperating.
• Taiwanese board makers routinely start production in China and finish the work in Taiwan, because Taiwan alone lacks enough capacity.
• US bans on Chinese-made goods make that split production legally murky, and regulators have not said where the line is.

Outlook: More companies could be pulled in until Taiwan's authorities clarify whether finishing Chinese-made parts at home counts as "made in Taiwan."