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When Size is Everything: Reeeeally Big Flex Circuits
June 25, 2008 |Estimated reading time: 10 minutes
Flexdude in Space: Working on the Mars Science Laboratory
This past year I had the great privilege of working with the good folks down at the Jet Propulsion Laboratory as part of a team working on the flex circuits going into the Mars Science Laboratory - the biggest, most complex Mars rover ever. It is scheduled to be launched in the fall of 2009.
It was fun to be part of such a big, high-profile project even though my part of the program was small: double-checking and reviewing flex circuit designs. The Mars Science Laboratory (MSL) is about nine feet long and dwarfs the previous two rovers (see picture on page 2). It has much, much more scientific equipment that will enable it to sample more types of soil and rocks. It will also be able to travel much further than the 2003 rover.
Figure 1. About the size of a small car, the Mars Science Laboratory rover carries an impressive amount of scientific equipment to evaluate rocks and soil. Image courtesy of NASA/JPL-Caltech. The flex circuits for the MSL build on the success of the previous two rovers and play an important part in packaging all this functionality into a very compact, very mobile robot. There is much more info on Mars Science Laboratory on the JPL Web site - http://marsprogram.jpl.nasa.gov/missions/future/msl.html.
Flex circuits are usually fairly small compared to rigid PCBs, and some of them can be very small. But what if you need a big flex circuit? I mean a really big flex circuit, five feet long or more?
While there are some design issues unique to large flex circuits, a bigger issue can be finding vendors - a flex manufacturer with equipment that can process large flex circuits and a materials supplier that can provide flex material in either rolls or very large sheets.
I have designed a handful of these oversized flex circuits for research projects in the past, and while working on the Mars Science Laboratory project I learned of new vendors that have the stuff necessary to make these reeeeeally big flex circuits.
Large Panel or Step-And-Repeat Processing?
Large panel processing is exactly what it implies - imaging, developing and laminating panels that are larger than 24X36 inches. Step-and-repeat uses standard equipment to process one section of the panel at a time.
If your vendor uses step-and-repeat processing, it is good to keep the line widths and spaces as wide as possible, at least 10 mil lines and spaces. This increased width allows for slight misalignment as the flex material is moved and repositioned in the imager. Coverfilm lamination can also be done in a step process, but there will be some oxidation at the boundary of the lamination press -- be sure that your application can live with this oxidation. On the plus side, the step-and-repeat process has no length limit - you can make circuits 40 feet long or more with no splicing. On the minus side, you're usually limited to two copper layers.
Large panel processing involves oversized equipment that can generate large-format artwork, image, develop and laminate the large panels with no stepping. The flex vendors that have this large equipment in-house are few and the size of panels that they can process varies. Fortunately, there are outside sources that can provide these services on some of the very largest panel sizes.
Materials
Whether your vendors intends to use step-and-repeat or large panel processing, they first have to get material for these monster flex circuits. If you only need 0.5 oz. or 1.0 oz. copper, many vendors, such as Rogers and Nippon Steel, can supply both adhesive-based and adhesiveless laminates in large rolls.
DuPont laminates, however, are only available in sheets, regardless of the copper thickness. DuPont can supply adhesiveless AP laminates in sheets up to 24X100 inches, and they can supply LF and FR adhesive-based laminate in sheets up to 24X50 inches. If the customer wants to use DuPont LF or FR materials in sizes larger than 50 inches, the vendor must build the base material from coverfilm and copper foil. Fortunately the coverfilms and freefilm adhesives come in rolls.
Figure 2. The Jet Propulsion Laboratory designs rovers like these, and they use plenty of flex circuits. Image courtesy of NASA/JPL-Caltech. But what if the customer really needs an unusual laminate? Fralock, a specialty distributor in Southern California, can custom-make large sheet of adhesiveless or adhesive-based laminates. Because of their relationship with DuPont, Fralock can get Kapton in unusual sizes and thicknesses, and the company has a large autoclave to create custom laminates.
Prototype Vendors
I found two prototype vendors that will tackle these extra-large flex circuits: Q Flex in Southern California and All Flex in Northfield, MN.
All Flex is both a quick-turn prototype and medium volume flex vendor. They market their extra-long flex circuits under the trade name Maxi-Flex. All Flex has upgraded their imaging and development equipment so that they can image a 24X96 inch panel. They use the step-and-repeat method for lamination.
All Flex is the only proto shop in the USA I know that builds copper-on-polyester flex circuits, and they have made some Maxi-Flex circuits using polyester materials. All Flex also recently invested in automated SMT assembly equipment to provide complete flex assemblies.
Q Flex, located in Santa Ana, CA, makes these large flex circuits in large panel format. They have a custom-made autoclave that can laminate panels up to 14 feet long and 14 inches wide. For several years they have produced a 107 inch long flex for an aircraft wing application. Being able to laminate these extra-long panels in an autoclave also gives Q Flex the ability to make long, multilayer impedance-controlled flex circuits with no splices.
This custom autoclave can be extended to laminate panels even larger than 14 feet. For panels that are wider than 14 inches, Q Flex has access to another autoclave that can handle panels up to 36X96 inches.
Q Flex doesn't have in-house capability to image and develop large-format artwork, but the company has vendors in Southern California who can. Q Flex is a very fine proto shop - I have done business with them for almost 10 years and recommend them often.
Production Vendors
Production vendors have more capabilities, but are more careful about what opportunities they take on. These jumbo-sized flex circuits are often made in low-production volumes that consume many hours of engineering, so this careful scrutiny of the flex opportunities is understandable. These vendors also tend to be suppliers to the military-aerospace industry, and their costs tend to be higher than those that cater to high-volume consumer products. That said, if you're looking for 2X6 foot flex circuits, you know they were not going to be $10 a piece, right?
First, let's look at Pioneer Circuits in Santa Ana, CA. Pioneer builds almost exclusively military and aerospace flex circuits, and they are famous in the flex world for creating very complex flex circuits for the first Mars Rover Sojourner. The flex circuits that went up in the Sojourner rover were 26-layer and 30-layer rigid-flex circuits needed to solve space and weight problems. Pioneer also built the flex circuits for the Mars Rovers that went up in 2003 - and they're still working!
Pioneer has a large autoclave capable of laminating panels as big as 24X90 inches, with the ability to image and develop panels up to 30X144 inches. More importantly, Pioneer has loads of engineering talent with lots of experience building these very long flex circuits. They have also developed techniques to splice these long flex circuits together, creating controlled-impedance flex circuits upwards of 30 feet long.
There are loads of information about the Mars space program flex circuits and other aerospace programs on the Pioneer Circuits Web page at www.pioneercircuits.com.
Minco produces flex circuits for the mil/aerospace industry, but they also have a presence in the commercial and industrial markets. I visited their facility back in 2005 (see the May 2005 issue of Flex Circuit News). Minco has a large autoclave for laminating large flex panels up to 72 inches long, and can image and develop these panels in-house. In addition to the flex circuit division, Minco also has divisions that make heater flex circuits, temperature sensors and instrumentation. Like Pioneer, Minco has bunches of engineering talent to draw from.
I was already familiar with both Pioneer Circuits and Minco, but while working at theMars Space Laboratory I learned about three more companies that have large panel capabilities: Speedy Circuits, Dynaco and Amphenol Printed Circuits.
Speedy Circuits of Huntington Beach, CA is very similar to Minco - they produce complex flex circuits for both the mil/aerospace and the commercial/industrial markets. They have a very large autoclave - 40X100 inches - so they can laminate a panel as large as 36X96 inches. Their etching capability is limited to panels 24 inches wide and their in-house imaging capability is limited to 20X30 inches, but they have access to outside services that can image and etch larger panels.
Speedy also has laser and gold, palladium and solder plating in-house. They plan to expand into the quick-turn prototype business, concentrating on turning simple rigid-flex prototypes within a week.
Amphenol Printed Circuits was formally known as Advanced Circuit Technology (ACT) in Hudson, NH. They were best known for their development of Sculptured flex circuits, a technique which takes very thick copper and selectively makes both thick copper features for interconnection (such as pins or lugs) and thin copper traces in areas where the circuit will flex. Amphenol also manufactures standard flex circuits and rigid-flex circuits for the mil/aerospace and commercial/industrial markets.
Amphenol doesn't have an autoclave, but has an oversized lamination press that can fit a 24X54 inch panel, certainly large enough for many applications. Amphenol has the capability to image and develop panels that size in-house.
Finally, Dynaco in Arizona builds complex flex and rigid-flex for both mil/aerospace and commercial/industrial customers. Dynaco's in-house lamination presses are about 34X38 inches, but they do have access to a lamination press that is 36X78 inches right across the street at Neltec, a very large PCB laminate manufacturer. All other processes and assembly can be handled in-house. Dynaco also has a unique capability to produce microwave rigid-flex circuits and bookbinder flex circuits.
So What About Your Industry?
I suspect many folks are saying to themselves "That's nice, but I don't work in aerospace. What good are these oversized flex circuits to me?"
Well, gasoline is moving towards $5.00 a gallon. Diesel fuel is worse - I'm looking at converting my diesel pickup to burn used French-fry oil. As the cost of energy soars the economics of many industries are changing. Car and truck makers are going to have to make vehicles smaller and lighter - exactly the same reasons that mil/aerospace folks use flex circuits! The solar power and medical industries are also changing; maybe your industry is too. So much so that an extra-large flex circuit can make sense? We'll see!
About Flex Circuit NewsThe Flex Circuit News is an industry newsletter published quarterly by Tom Woznicki of Flex Circuit Design Co., and republished here with permission. Flex Circuit News is dedicated to providing information about all aspects of and promoting the use of flexible printed circuits in interconnection and electronic packaging. The Flex Circuit News is a free publication, delivered to subscribers by e-mail since 1997.Click here to read this edition of the Flex Circuit News in its original format, or go to www.flexdude.com. Got a question? Send an e-mail to Tom at tom@flexdude.com or call 408-629-8343.About Flex Circuit Design Co.
Flex Circuit Design Co. is a consulting company in San Jose, CA founded by Tom Woznicki. Flex Circuit Design Co. specializes in designing flexible printed circuits for OEMs and flex circuit manufacturers. (c) Copyright 2008, Flex Circuit Design Co. All rights reserved. Flex companies named in this columnFralock28525 W. Industry Dr.Valencia, CA 91355Phone: 661-702-6999Toll free: 800-372-5625Fax: 661-702.9899www.fralock.com
All Flex Inc.1705 Cannon LaneNorthfield, MN 55057Phone: 507-663-7162Fax: 507-663-1070www.allflexinc.com
Q Flex Inc.1301 E. Hunter Ave.Santa Ana, CA 92705Phone: 714-664-0101Fax: 714-415-5529www.qflexinc.com
Pioneer Circuits3000 S. Shannon St.Santa Ana, CA 92704Phone: 714-641-3132Fax: 714-641-3120www.pioneercircuits.com
Speedy Circuits5331 McFadden Ave.Huntington Beach, CA 92649Phone: 714-898-4901Fax: 714-891-0607www.speedycircuits.com
Minco7300 Commerce LaneMinneapolis, MN 55432Phone: 763-571-3121Fax: 763-571-0927www.minco.com
Amphenol Printed Circuits91 Northeastern Blvd.Nashua, NH 03062Phone: 603-880-6000Fax: 603-880-1785www.act-flexcircuit.com
Dynaco Corp. 1000 South Priest Dr.Tempe, AZ 85281Phone: 480-968-2000Fax: 480-921-9830www.dynacocorp.com