Bookings were up 62.4% from a year ago and shipments were up 41.3%, said IPC, which administers the monthly poll. The figures may include some sales of products built offshore and brokered by the surveyed companies.

The book-to-bill ratio for all baord types was flat at 1.11. 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 1.11 means that for every $100 in shipments, $111 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 50.3% while shipments are running 36.3% higher, IPC said.

However, the overall data obscure an unsettling trend: a drop in demand for rigid product. The 90-day book-to-bill for rigid boards was 0.95 in May, and the 30-day B2B was 0.90, according to estimates.

The May PCB shipment index rose 5.5% sequentially to 138.7.

The booking index was up 23.8% to 168.8.

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 43.8% in May over last year, and orders jumped 67% year-on-year.