The book-to-bill ratio rose to 1.12, up 0.04 sequentially. The ratio is calculated by averaging the number of orders booked over the past three months and dividing by the average sales billed during the same period.

A ratio of 1.12 means that for every $100 in shipments, $112 worth of PCBs were booked. An increasing ratio is generally considered a sign of a market poised to rise.

For the year, bookings are up 42.8% while shipments are 32.6% higher, IPC said.

The January PCB shipment index rose 15.3% sequentially to 151.5. The booking index was down 2% to 160.9, IPC said. An index of 110 indicates 10% growth over the same period in 1992.

The indices are calculated by setting the base year (1992) equal to 100 and then multiplying the monthly growth rates of the actual shipments and bookings by the corresponding index number. According to IPC, the index takes into account changes in the size of the industry.

Based on "same store" data -- a measure of those companies that reported last year and this year -- PCB shipments grew 32.9% in March over last year, and orders have risen 37.1% year-on-year. Year-to-date, survey participants report shipments have increased 30.2% and bookings are up 41.1%.