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Featured Article

Beyond Epoxy: High Performance Thermosets Part Five, Electronic Packaging

May 30, 2023 By Jeffrey Gotro

The previous post covered an introduction to cyanate ester thermosetting resins. This post will discuss the main applications of cyanate ester thermosets.  In the 1980’s the main applications for cyanate esters were in electronic applications. Specifically, cyanate esters were used in high performance circuit boards and semiconductor substrates.  The substrate technical drivers are:

  • Lower coefficient of thermal expansion (CTE), specifically low z-axis expansion
  • Low dielectric constant (Dk < 4) and low dissipation factor (Df< 0.01) over a wide frequency band
  • Adhesion to low Dk/Df resins
  • Thinner cores that enable smaller vias for high density routing
  • Low warpage for thin flat substrates

The primary substrate core supplier is Mitsubishi Gas Chemical (MGC) and has supplied the industry with bismaleimide triazine (BT) laminates since the early 1980’s.  MGC BT is a proprietary blend of bismaleimide, cyanate ester (triazine) and epoxy [1].  MGC provides a wide range of copper clad laminates (CCL) and prepregs.  The CCL HL832NX (laminate) and GHPL-830NX (prepreg) are the standard halogen-free BT with a flammability rating of UL94V-0.  Click for a complete listing of the MGC BT product offerings.

The chemistry of the bismaleimide triazine (BT) resin is shown in Figure 1.

Figure 1. Chemical components of MGC BT resin systems [1].

In Figure 1, the chemical structures are given for the three main components of BT laminates are prepregs.  Owing to the high glass transition temperatures for the fully cured BT laminates, aromatic bismaleimides were used as shown in the top image.  The MGC patent describes a large variety of bismaleimides that can be used.  Cyanate esters are interesting in that they have very low dielectric constant and more importantly have a low dielectric loss factor.  The cyanate functionality undergoes a cyclotrimerization reaction leading to a triazine ring structure.  The most common cyanate ester is synthesized from bisphenol A to form the aromatic monomer.  After trimerization, a very high Tg is obtained.

The third component of the BT resin system is epoxy.  Epoxy monomers are available in various monomeric forms, from liquid epoxies to novolac epoxies, to the common Bis-A epoxy (as shown in the bottom in Figure 1).  Epoxies are also available in several molecular weights.  The curing package for epoxies is typically diamines.  It turns out that diamines are also useful curing agents for the bismaleimides via the Michael addition reaction to the bismaleimide double bonds.

The MGC patent [1] also describes various amines that can be useful in tailoring the physical properties of the BT resin system.  In the ‘MGC patent, example 11 shows a typical BT formulation with 10 parts by weight bismaleimide, 20 parts by weight cyanate ester and 70 parts by weight epoxy (DER 542) and 3 parts by weight of an amine curing agent, 2-ethyl-4-methylimidazole (24EMI).

Cyanate esters have found applications in aerospace due to their low loss properties.  Cured cyanate esters have dielectric loss factors in the range of 0.008.  The use of low dielectric loss factor quartz fibers enables aircraft radomes [2] as shown in Figure 2 below.

Figure 2.  Low dielectric loss cyanate esters used with quartz fibers in an aerospace radome application [2].

Cyanate esters are used in a wide variety of applications owing to the large toolbox of monomers, oligomers, curing agents, accelerators available to the formulator.  As seen in this series of posts, a large majority of commercially viable products are blends of the various types of bismaleimides and cyanate esters.  The formulator’s task is to evaluate the physical properties required and then tailor the chemistry and curing reactions to achieve the desired products.

References

  1. US Patent 4,110,364, Morio Gaku et. al.
  2. Cyanate esters for radomes
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More From the Blog

Beyond Epoxy: High Performance Thermosets Part Four – Cyanate Esters

May 15, 2023 By Jeffrey Gotro

The previous posts in this series covered various types of bismaleimide resins and formulations.  The next three posts will discuss cyanate ester resins and formulated products. Dicyanate resins, alternatively known as cyanate ester resins, describes both a family of monomers and oligomers with ... [Click to Continue...]

Beyond Epoxy: High Performance Thermosets Part Three – Liquid Bismaleimides

May 1, 2023 By Jeffrey Gotro

The previous two posts covered aromatic BMI resins and curing mechanisms leading to highly crosslinked and high Tg thermosets.  Another important class of bismaleimides are liquid bismaleimides.   Liquid BMIs with long-chain aliphatic structures between the maleimide groups are used for low modulus, ... [Click to Continue...]

Beyond Epoxy: High Performance Thermosets Part Two – Bismaleimide Cure Chemistry

April 17, 2023 By Jeffrey Gotro

This post is part two in a series on high performance thermosets and will cover aromatic bismaleimide curing chemistry. Bismaleimides are thermosetting polyimides that cure by addition reactions that avoid formation of volatiles. Unlike condensation polyimides (such as DuPont Kapton® or Ube ... [Click to Continue...]

Beyond Epoxy: High Performance Thermosets Part One

April 3, 2023 By Jeffrey Gotro

Epoxies have been a workhorse in the thermoset industry for decades. They offer a compelling cost/performance benefit in many applications.  This blog post series will cover other high performance thermosetting resins such as bismaleimides and cyanate esters.  Bismaleimides can be aliphatic such as ... [Click to Continue...]

Accelerators for Amine Curing Agents

February 13, 2023 By Jeffrey Gotro

Guest Post by Jeremy Pasatta, Advanced Polymer Coatings Amine curing agents are still considered the largest class of curing agents for epoxy resins, and they are often used in demanding applications that require fast return to service or curing in less than ideal environments, such as very low ... [Click to Continue...]

Accelerators for Anhydride Cured Epoxies

January 30, 2023 By Jeffrey Gotro

Guest Post by Jeremy Pasatta, Advanced Polymer Coatings Anhydride curing agents for epoxies are a popular choice amongst formulators because they give the final cured formulation very high thermal properties along with excellent electrical properties, and their high use level and low viscosity ... [Click to Continue...]

Accelerators for Latent Epoxy Curing Agents

January 16, 2023 By Jeffrey Gotro

Guest Post by Jeremy Pasatta, Advanced Polymer Coatings Latent curing agents for epoxy resins allow for the creation of stable one component formulations used in adhesives and composites that have outstanding high temperature and mechanical properties.  In order to activate the latent curing ... [Click to Continue...]

New Book Chapter

January 11, 2023 By Jeffrey Gotro

I am pleased to announce that Dr. Gotro and Dr. Prime have recently published a book chapter in the ASM Handbook. Characterization of Thermosetting Resins and Polymers By: Jeffrey Gotro and R. Bruce Prime The chapter is available at ASM Handbooks Online. Click here to access This article ... [Click to Continue...]

Polymer Innovation Blog

I’m Dr. Jeff Gotro and welcome to the Polymer Innovation Blog. Over the last 40 years I have been involved in polymer research, along with product and process development. I acquired invaluable experience working for IBM, AlliedSignal, Honeywell and Ablestik Labs (now Henkel). In this blog, I (along with some guest contributors) will share our experiences, tips, and “tricks of the trade” to get more out of your innovation efforts and discuss new trends and technical advances in the polymer industry.
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