When Will That Elusive Liquid Crystal Film Polymer Market Break into the Big Time?

Estimated reading time: 10 minutes

It's coming sooner than you might think, and, when it does, LCP films will be the universal substrate, crowding out polyimide, epoxy glass, and a few others.

Robert Jung, President of Altaflex, a flexible circuit fabricator in Santa Clara California, told me the other day, "If LCP films were available in quantity from multiple vendors, they would take off like wildfire." Judging from the amount of IP resulting from R&D in LCP films, Robert is not alone in so describing the potential for LCP films. Today, the reality is limited supply and premium prices, higher than the dominant, but parametrically inferior, polyimide film. PI absorbs water, degrading performance at high frequencies. LCPs do not absorb water, and are superior in Dk and Dissipation Factor, flat to over 45 gigahertz. That allows closer spacings, higher density, with less crosstalk. Heat stability is also superior. A wide range of polymers may be rendered in liquid crystal state, some very inexpensive, like polyester, whose basic cost is one-tenth that of PI. What's holding LCP films back?  New materials present new problems.

All that growing IP is directed at new solutions that will level those processing barriers now restraining the market development of LCP films. We'll take the pulse of the increasing activity on the Technology Push side with the help of a recent patent application that provides a timeline for major steps in leveling those bad new barriers. The selected patent application also provides insight into one of several Market Pull factors that will make Robert Jung's prediction come true. HDD technology is about to undergo a major transition for market survival of magnetic disk drives against the flash memory onslaught. That will facilitate LCP film replacement of polyimide in that next HDD generation. That's just one beginning; the ultimate benefit to the electronics industry of LCP films universal substrate usage will extend far. The beneficial implications include supply chain simplification, lower circuit material and fabrication cost, superior performance.

LCP properties and the few remaining barriers to widespread production and usage in film form are a byproduct of their molecular structure. There is no shortage of liquid crystals in Nature. You, the reader, are in large part, a collection of liquid crystals--your muscles, your cell walls, your DNA. LCs are a fourth state of matter, between solids and liquids, technically neither solid crystalline nor isotropic liquid. Their molecules are lined up in multiple single file order with no restriction on positional relationship of the files. That's what endows them with optical properties for displays and why muscles shorten and swell as they lift or push, but, for films, that directionality results in anisotropy, Longitudinal characteristics differ from extrusion dimension characteristics, presenting an early stumbling block to circuit usage.

3M's WO/2003/077622 patent application, "LIQUID CRYSTAL POLYMERS FOR FLEXIBLE CIRCUITS, following the usual protocol, presents a thread of prior art that leads to its unique invention disclosures. Thus it presents a useful history of advances along a chosen path. I will also discuss an alternative path, which is historically important. But it is the match between 3M and its allies in one corner, Hutchinson and Rogers in the other, for victory in the suspension flex war for future perpendicular disk drives, that has the drama. LCP films are going to win that match. We'll start with the Business story; In the Technology story, the coming LCP victory is a slam dunk.

The Disk Drive industry is very mature and becoming more oligopolistic every day, the two phenomena do go together, just as it says in Econ 101. Seagate-Maxtor, with $14B in 2007 sales, has 40% of the market. Western Digital has 20%; Hitachi, Toshiba, and Samsung share the rest.

At the low end, semiconductor flash memory is a threat, forcing Hitachi to leave the micro-disk, one inch form factor market. The failure of the tiny drive market impacted Magnecomp's suspension business adversely. TDK recently bought Magnecomp for half its sales value, enabling it to be a complete subsystem supplier with its magneto-resistive heads. Hutchinson dominates the suspension chem milling and flex circuit business with about $800M sales, a 60% market share. Their biggest customer has been TDK, which just bought their biggest competitor, Magnecomp. But with the departure of Innovex from the suspension flex market, Hutchinson sales to Seagate will increase. Seagate makes its own heads.

The best is yet to come. Many have prematurely declared the death of the disk drive industry, to be replaced by IC memories. But magnetic drives have another trick up their spindles. It is perpendicular recording, capable of delivering 10 times the storage density of present longitudinal recording, one terabit per square inch. No funeral soon. Perpendicular recording will require complete head suspension and flex re-design. 3M is aiming at the suspension flex $300M + market with some very neat technology, including LCP films. It's time to get back to the Technology story of LCP films. Technology Push and Market Pull will muscle LCP films into the mainstream in suspensions and lots of other places. I told you that muscles are liquid crystals.

The 3M patent application cites prior patents that address 3 major LCP film processing problems: 1) the x-y asymmetry, 2) bonding to copper and other LCP film layers, film etching. In 12/1990, Foster-Miller, the Boston think-tank, was granted a multi-axial patent, U.S. 4975312. "A combination of rotational shear and elongational flow during the extrusion process orients the LCP molecules."

"To understand the tailorable CTE of XYDAR(R) or VECTRA (R) molecularly oriented polymer films, it is necessary to review the processing and morphology of these materials.

During, the orientation step, the rod-like molecules of XYDAR(R) or VECTRA (R) are formed into a microfibrillar network with homogeneity down to a very fine scale. It has been discovered that the dimensions of this microfibrillar network are on the order of about 100A. Thus, the self-reinforced material will appear continuous to the relatively large electronic components, printed conductors and other features of the electronic package.

After the XYDAR(R) or VECTRA(R) film has been finished by drying and heat treatment, the mechanical properties are consistent and repeatable and the film shows excellent environmental stability including low moisture pickup (less than 0.5 percent by weight after 24 hr. immersion at 25* C.) " Point 3), etching LCP films has been furthest developed and disclosed in the 3M patent. Tapered vias can be etched, similar to back drilling to reduce signal reflections. No drilling or punching is necessary. 3M is strengthening its position as a flex circuit fabricator. The strategy is to capture high value-added product markets. Disk drive suspension interconnect is a target.

The main barrier to scaling up production of LCP for wider use remains the adhesive problem. Today it is accomplished by pressing the thermoplastic films at over 260C, actually melting at the surface, a hard to control, unpredictable process. Typical of efforts toward a solution is a statement by Rogers, "To achieve uniform lamination of LCP films, lamination equipment must be capable of producing high temperature and pressure conditions in an accurate and uniform manner. Such equipment is costly and has proved to be a barrier to widespread application of LCP film in printed circuits, particularly multi-layer circuits. EP 507 332 discloses how to make a laminate comprising a liquid crystalline polymer using roll lamination, but does not disclose a pretreatment to adjust the coefficient of thermal expansion (CTE)." Rogers, United States Patent 6602583, 8/2003.

Out in the wings, a company that I may not mention is developing a "molecular bonding" molecule, like Liquid Crystals, straight out of biology. It may be possible to incorporate it in a bonding sheet. It is said that it will bond anything to anything.

Companies delivering LCP films include Hoechst Celanese, Rogers-Kuraray, W.L. Gore, But work is being done by many others: Sumitomo Chemical, Toray, Denso, Nippon Steel, DuPont, etc.

In the early 1990s Teledyne Electronic Technologies used LCP films as substrate for flex circuits in an aircraft black box, a continuing use. They use a hot roll for laminating. 

Dynaco, a flexible circuit fabricator in Tempe AZ (US), has a trade secret for bonding LCP films, even to PTFE.UC Davis has an active program building microwave circuits using LCP films:

Microwave LCP film references from UC Davis--2006, 2007A. Pham, A. Knoesen, D. Roitman, and Z. Wei, "Microwave Electromagnetic Band Resonator Bio-sensors," pending 2003.

Design and Development of a Package Using LCP for RF/Microwave MEMS SwitchesChen, M.J.; Pham, A.-V.H.; Evers, N.A.; Kapusta, C.; Iannotti, J.; Kornrumpf, W.; Maciel, J.; Karabudak, N. Microwave Theory and Techniques, IEEE Transactions on Volume 54, Issue 11, Nov. 2006 Page(s):4009 - 4015 Digital Object Identifier   10.1109/TMTT.2006.884639

We present the development of an ultrahigh moisture-resistant enclosure for RF microelectromechanical system (MEMS) switches using liquid-crystal polymer (LCP). A cavity formed in LCP has been laminated, at low temperature, onto a silicon MEMS switch to create a package. The LCP-cap package has an insertion loss of less than 0.2 dB at X-band. E595 outgas tests demonstrate that the LCP material is suitable for constructing reliable packages without interfering with the operation of the MEMS switch. The package also passes Method 1014, MIL-STD-883 gross leak, and fine leak hermeticity tests

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/22/36141/01717772.pdf

Microwave Microsystems Laboratory....University of California, Davis

Source: http://www.ece.ucdavis.edu/mml/pages/sponsors.html

Reference: Professor Anh-Vu Phamhttp://www.ece.ucdavis.edu/mml/papers/pham_cv_UCD_wb.pdfpham@ece.ucdavis.edu

Since 2003, we have investigated liquid crystal polymer to develop a hermetic organic packaging platform. Hermetic packaging is required to achieve high reliability for both MMICs and RF MEMS. Current state of the art hermetic packages employ metals, ceramics or Si to form an enclosure that is typically sealed using laser welding or high temperature wafer bonding. These materials and sealing processes add significant weight, size, and cost to a system. In collaboration with GE Global Research Center, we have developed a novel process to laminate liquid crystal polymer films onto Si. This process is used to develop hermetically sealed cavities for RF MEMS switches [http://www.ece.ucdavis.edu/mml/papers/J11.pdf, C1, C9, and C15] (Figures 2 and 3). This newly developed technology has the potential for solving the fundamental problem of RF MEMS packaging and brings RF MEMS devices into usable systems at affordable cost. Using this packaging process, we have designed and implemented a 2-bit phase shifter with RF MEMS switches in a multi-layer organic module and a wideband amplitude compensated true time delay circuit ["http://www.ece.ucdavis.edu/mml/papers/J1.pdf", C1, and C2] (Figures 4 and 5). We have also developed novel multi-layer organic hermetic surface mount packages at Ka-band frequencies (Figures 6 and 7). The feedthrough of these surface mount packages achieves less than 20dB return loss at Ka-band frequencies [C3 and "http://www.ece.ucdavis.edu/mml/papers/C10.pdf"]. The result of this research demonstrates that it is possible to use low cost organic hermetic surface mount packages for millimeter wave frequencies. Our paper at the IEEE International Microwave Symposium was selected as Student Finalist in the Student Paper Competition. We have demonstrated that LCP packages can provide a fine leak rate of less than 5X10-8 atm-cc/s, which passes hermetic requirements by Method 1014, MIL-STD-883. The big question is whether these organic packages (while passing the hermetic fine leak rate) can achieve the same reliability as that of metal and ceramic packages. If so, the results of this research will make significant impact on microelectronic and sensor industry. On-going research is to investigate the reliability of these hermetic LCP packages and to scale electrical performance to 110 GHz operation. 

Summary--Perspectives for LCP Films in Printed Circuits

Today, LCP film flexible circuits address niche markets, limited by availability and high material costs. These realities have influenced the negative perceptions of many. But the record shows that, one by one, LCP technology hurdles have been vanquished. .Even further, in film etching, superiority has been demonstrated. One hurdle remains--bonding. Hot presses to melt the material are not an acceptable way for multi-copper layer construction because of unpredictable dimensional changes to dielectric and conductor.

The implications for electronic interconnection of scaled-up, mass production of LCP films extend beyond flexible circuits of today. Consider the prospect of LCP films, as carrier of traces in Occam constructions, with components in their own compartment, connected by copper plated blind vias. The potential replacement of the $2.2B polyimide market but also the $10+B rigid substrate material market by a material lower in cost--that's the narrow view. The real potentials are for standardization of materials and simplification of the fabrication process, in old and new applications. There are pressing needs for cost reduction. Ultimately, demand elasticity plus electronic equipment innovation will expand substrate and all electronic hardware markets. LCP films will be an important enabler of that process.