Custom high-speed backplanes aid in making new products
By Ed Garstkiewicz, market & applications manager for broadcast, medical and military, Harting Inc. ofInterconnect
Achieving ultra-fast data transfer rates, the equivalent in advanced electronics to supersonic travel, is a critical threshold for designing the next generation of sophisticated products like medical imaging systems or broadcast routers.
Only a complex custom backplane that employs suitable pcb base materials and interconnect systems under proper design rules can deliver the exceptional data throughput rates that make possible the breakthrough capabilities of many new products. Today’s fastest custom backplanes can deliver over 25 Gigabits per second serial. Developing these complex boards involves collaboration between the customer and one of a relative handful of manufacturers specializing in and equipped to assemble custom backplanes.
In creating an ultra-fast board, the backplane specialist can supply signal integrity analysis and modeling of the entire channel from chip-to-chip to determine the optimal layout and routing in conformity with the latest standards for high speed transfer. This specialist firm has design capabilities of its own, but more often than not works with the customer’s engineers or consultants to arrive at the best achievable configuration – also the right balance between costs and performance for the product for which it’s destined. The custom backplane assembler then coordinates the network of specialized vendors – pcb, tooling and component manufacturers – with the expertise to support such a custom build.
Harting’s North American backplane manufacturing facility in Elgin IL has begun full production of its largest backplane ever – 46 inches long, 62 layers (over 3/8 inches thick) with 17,000 contact points. This requires equipment large enough for handling such an oversized product: screen printer, pick and place and press-fit machines, reflow oven and advanced testing facilities. Most backplane manufacturers typically work on an 18 x 12 inch surface, whereas custom builders usually can handle boards as large as 48 x 24. For ultra-fast backplanes, thickness presents another manufacturing challenge that requires special expertise; the greater the transfer rate, the thicker the board and the harder it is to solder.
Large custom boards tend to have components affixed by both soldering and press-fit methods. Press-fit technology is not something a lot of manufacturers understand or know how to do. Doing it wrong can damage components or render the entire backplane a costly piece of scrap. The Elgin plant has two semi-automatic press-fit machines and one fully automatic machine, all built by Harting. Each tests the insertions as they are made. If a connector is not inserted properly – if a pin collapses, gets bent or folds under – incorrect force may be applied. The machine sends an alarm if there’s too much or not enough force. Insertion data is archived for 15-years, so if a problem develops in the field, the data can be reviewed to determine how each component was installed on that board.
The RoBAT test system is the gold standard for testing a finished custom high=speed board. RoBAT can handle backplanes of virtually any dimensions. During RoBAT testing, each backplane undergoes continuity and isolation tests to ensure the connections are correct and there are no shorts or opens on the board. The RoBAT system is extremely accurate and can detect defects within the pcb. An AOI test examines all components to make sure they are all placed and oriented correctly. As part of the AOI test, the RoBAT also performs a bent pin test: if there are any male connectors on the board it will make sure the pins are straight, not off-centered. The RoBAT will also perform a DMM test ensuring resistors on the backplane are the correct value.
It doesn’t appear that the development of electrical backplanes has reached a definitive performance limit. For years, there have been predictions that the industry couldn’t do much more with copper laminate than it had done already – that speeds above 10-15Gbps would mean going for an optical backplane, a promising concept that still needs a great deal of additional development before it becomes a cost-effective, reliable alternative to an electrical board. Instead, we are likely to see 40Gbps or more on copper laminate. Pcb manufacturers keep increasing their capabilities to make even more complex printed circuit boards. Connector manufacturers keep pushing more speed through connectors. The likelihood is that custom copper laminate backplanes will keep pushing the speed envelope so OEMs can take their products to yet another level.