BANNOCKBURN, IL, Oct. 29 -- September bookings of printed circuit boards continued to outpace billings in North America, according to the latest 90-day moving average of manufacturers.

The book-to-bill ratio for all types of boards was 1.08, meaning for every $100 of shipments, $108 in orders were booked, said IPC, which tracks the data. The trade group does not disclose the participants or their revenues. The book-to-bill ratio was 1.04 in August.

The ratios for rigid and flex boards were 1.01 and 1.38, respectively. The ratio is calculated by dividing the value of orders booked over the past three months by the value of sales billed. A ratio over 1.0 is considered an indicator of rising demand.

Overall September shipments rose 25.9% and bookings were up 18.1% year-on-year, IPC said. For the year, shipments are up 33.5%, bookings are up 35.2%. Sequentially, shipments were up 12.1%, bookings 16.6%.

"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 the month rigid PCB shipments were up 12.2% but bookings fell 10.1%. Flexible circuit shipments were up 85.6% and bookings were 140.1% higher.

Year-to-date, rigid PCB shipments are up 23.3% and bookings are 16.8% higher, while flex shipments have grown 78.5% and bookings are up 106.5%.

The flexible circuit sales include some value-added services -- about 17%, says IPC.