LCP: A Thermoplastic Phoenix
Steve DeWaters
Leading Market Innovation in Nex-Gen Electronics at Precision Circuit Technologies.
In my last article ‘The Big Shrink’, I indicated the need for printed circuit materials that can accommodate emerging 5G and sub-6G frequencies and data rates.
Conventional materials and subtractive chemical processing are meeting their functional limits for providing higher frequencies and faster data rates that accompany next-generation applications. And presently, those applications are leaping from designer’s computer screens.
Semi-additive (SAP) and Modified Semi-Additive (mSAP) processing – en route to Full Additive (FAP) – are the signposts for the development road ahead, but also for the printed circuit industry at large.
Enter Liquid Crystal Polymer (LCP), a thermoplastic organic material with impressive attributes that address many of the signal management concerns conventional materials simply cannot.
As early as 1995, Foster-Miller created a spinoff company, Superex Polymer, Inc., to promote LCP applications and stated then: “…it expects LCP film's first commercial use will be in laminations with copper foil for multilayer printed circuit boards and multichip modules.” (SUPEREX-ALLIANCE-TO-PROMOTE-LCP-FILMS | Plastics News)
Sixteen years later, Rogers Corporation announced the release of new materials, including their Ultralam 3850 LCP laminate and bondply materials (ULTRALAM? 3000/RO2808?/RO4000? | Microwave Journal). These were meant to address high-speed and high-frequency circuits mainly centered in the computer network and telecom markets at that time.
The PCB industry struggled with how to correctly process these LCP materials and found poor yields attending most attempts at producing boards. Sometime prior to the 2020-2021 COVID crisis, Rogers Corp. discontinued their LCP product as their customers could not find a consistent way to process the material without significant impacts to their cost/yield equations.
In 2009, HSIO Technologies was founded by James Rathburn and, with his LCP process patents, he established reliable solutions to the LCP processing dilemma and set out to apply those remedies in a small factory in Arizona.
The performance virtues and application range of LCP were also concisely framed in a 2014 published article by Rathburn on the EEWeb publication:
In 2016, the HSIO operations sold, and the patents licensed, to Benchmark Electronics under a strategy to create a captive board shop whereby LCP and other materials could serve emerging microelectronic and photonic assembly applications. It was a sound strategy, though less so in its implementation, as erecting the captive operation was fraught with a variety of issues for many months.
The concept did, however, begin to yield very good results in LCP products by mid-2021 and several customers were lining up with designs. Then, Benchmark’s corporate strategy changed, and the captive board manufacturing idea was summarily cancelled by executive fiat, leaving customers in the lurch.
In the aftermath of that idea’s demise, Rathburn sought to reconstitute the intellectual properties (IP) and to resurrect the notion that LCP remains an excellent material choice for the markets ahead.
Today, he has gathered the IP and formed a new company: Precision Circuit Technologies, LLC (PCT), to create new capabilities that address emerging high speed, high frequency market demands. Several licensed manufacturing partners will accompany this business model, positioning PCT as an advanced technology development entity, and channeling new materials, methods, and expertise into the partnerships for scaled manufacturing.
In this sense, LCP lives on and so does its notable characteristics. By comparison, LCP stack-ranks splendidly against other materials in categories such as:
DIELECTRIC CONSTANT
– Measuring the ability of a substance to store electrical energy in an electric field –
EFFECTIVE DIELECTRIC CONSTANT
SIGNAL SPEED
– The speed at which a wave carries information –
PROPAGATION DELAY
– The time duration taken for a signal to reach its destination –
领英推荐
In all these comparisons, the LCP performance excels. Besides the important electrical properties, LCP also has excellent resistance to chemicals, high strength and modulus, excellent flex/fold capabilities, low coefficient of thermal expansion (CTE), and low dissipation factor [Df: the inefficiency of material to hold energy or behave as an insulating material].
You’ll note a 'yellow' point on these graphs called ‘PLLD’ that exceeds even the LCP performance. This refers to an as-yet-unrevealed material/approach that is still undergoing various reliability tests. Perhaps another article downstream will unveil this.
The nature of LCP also permits signal geometries to dramatically shrink (well below 25 microns); allows shrunken board real estate (see scale comparison below), greater component densities, and gives rise to design alternatives that the limits of subtractive processing simply can’t produce.
LCP also allows the perfection of transmission line geometries in circuit boards. That is, the lines are made more uniform than ‘ragged’, and this promotes continuity of a signal in terms of mitigating: loss, skin effects, crosstalk, impedance mismatch, and other signal management factors. This makes LCP an excellent choice for current RF applications.
Moreover, LCP can accommodate 5G mmWave and sub-6G frequencies (20-100+ GHz) and signal speeds of 112-128 Gb/s, with work being done up to 224 Gb/s. These parameters challenge the physical limits of other materials, thereby leaving designers with only a few choices when deciding how to inaugurate their next-gen applications. LCP is an excellent option in that mix, and with old processing problems now mitigated by new approaches, it is also a readily available alternative.
So, what are some of the applications under development and for which materials such as LCP can prove useful? Here are a few that leap to mind:
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A Note About Ajinimoto Build-Up Film (ABF)
First used to package IC’s by a major semiconductor manufacturer in 1999, ABF is found in nearly every PC and Smart Phone in the world and has dominated the Pan-Asian markets as a go-to material choice for facilitating CPU performance.
It’s characteristics, until the advent of LCP, were largely unrivaled and some domestic U.S. board shops are presently trying to adopt ABF into their manufacturing strategies to accommodate some of the applications mentioned above.
PCB companies entering substrate application markets tend toward using of BT materials and/or copying the Asian approach for ABF. This is a sound strategy to create diversity in material offerings, but by adding LCP capabilities into the strategy, companies can leverage the same basic equipment set with much higher performance.
ABF is also sole sourced in Japan and as recently as Spring 2022, Ajinimoto had ABF shortages that catalyzed CPU, GPU and IC shortages, with negative global economic affects. DigiTimes Asia reports that such shortages could return in 2024 (ABF substrate shortage may return in 2024 (digitimes.com)).
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With such variables in play, LCP is a wise alternative to consider - for designers, manufacturers, and assemblers alike. Under this rationale, LCP is indeed rising from its erratic history and finding new traction.
It hasn’t been an easy road for anyone manufacturing circuit boards for the past several decades. Whatever can go wrong probably did at some point for industry participants. So, it’s only natural to find reluctance to shifting gears into adopting the SAP, mSAP and FAP methodologies needed to create the solutions for next generation signal management.
But it’s a tremendous opportunity for astute participants willing to pay homage to the halcyon days of yore and focus today on developing new capabilities that serve the markets ahead.
And the novel materials needed for the 5G and 6G (THz frequencies) application sets will need to be embraced as the printed circuit industry marches into the future, albeit with some industrial melancholy as ossified practices give way to the necessities of what the next markets demand.
?“We cannot solve our problems with the same thinking we used when we created them.”
Albert Einstein