Taiwanese chip substrate maker Unimicron is under criminal investigation, a negative surprise for a stock that hit a record high the same morning.

• Prosecutors in Taoyuan searched Unimicron's plant in the Guishan industrial district and confirmed the raid.
• Two vice presidents and an accountant were taken away for questioning, and four laptops were seized.
• Prosecutors have not said what the case is about, leaving investors guessing.
• Unimicron is one of Taiwan's three big ABF substrate makers alongside Nan Ya PCB and Kinsus, so the news is rippling through the sector.
• The stock touched an all-time high early in the day, then closed lower before the raid became public.

Outlook: The share price is likely to stay shaky until prosecutors explain what they are investigating.