NORTHBROOK, IL, Aug. 27 -- August orders for rigid circuit boards rose 8.7% while demand for flex circuits showed signs of weakness, according to the latest 90-day moving average of North American manufacturers.

"Both rigid and flex shipments are rebounding from the recession and are showing strong growth, but flex is growing at a faster rate than rigid," IPC said in a press release.

For all board types, shipments rose 33.6% and bookings were up 9.8% vs. a year ago, said IPC, which administers the monthly poll. The figures may include some sales of products built offshore and brokered by the surveyed companies.

The August book-to-bill ratio was 1.05 for rigid, up 0.06 points sequentially. The B2B for flex circuits fell precipitously, from 1.57 last month to 0.98 in August.

The book-to-bill for all board types rose fell 0.06 points to 1.04.

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 1.04 means that for every $100 in shipments, $104 worth of PCBs were booked. An increasing ratio is generally considered a sign of a market poised to rise.

Year-to-date shipments are up 34.7% and bookings are up 38%. Combined August shipments rose 13.8% sequentially, while bookings fell 0.3%.

August rigid shipments were up 21.9% and bookings 8.7% over last year. Year-to-date, rigid shipments are up 25.1% and bookings are up 21.1%. Among those surveyed, rigid shipments rose 15.2% sequentially and bookings were 7.6% higher.

August flex shipments were up 75.2% yet bookings slumped, falling 19.3% vs. last year. Year-to-date, flex shipments are up 77.4% and bookings 100.7%. Sequentially, flex shipments rose 8.5% and bookings dropped 27.1%.

Flex sales, which include some value-added services, make up about 17% of total PCB sales in the IPC poll.

The data come from a sample of North American rigid and flexible PCB manufacturers.