Arlon PCB Materials: Grades, Properties and Selection
What Arlon Materials Are
Arlon is a family of high performance laminates rather than a single material. The name covers several different resin systems made for different problems: radio frequency circuits that need a low and stable dielectric constant, high speed digital boards that need a low loss tangent, high temperature boards that need a resin which survives repeated thermal cycling, and power circuits that need a dielectric which conducts heat.
What the family has in common is that each grade is intended for an application where standard FR-4 is not good enough. Choosing one therefore starts with identifying which requirement the standard material fails, because a material selected for the wrong reason adds cost without solving the problem.
The Material Families
PTFE based laminates with woven glass. Polytetrafluoroethylene has the lowest dielectric loss of the common laminate resins and a dielectric constant below three, and it is essentially unaffected by frequency and temperature. Woven glass reinforcement gives it mechanical strength and dimensional stability, at the price of a dielectric constant that is higher than pure PTFE and slightly dependent on the glass content. These materials are the standard choice for microwave circuits, antennas and radar front ends.
Low loss thermoset laminates. Thermoset resins formulated for a low loss tangent with a higher dielectric constant than PTFE, and much easier to process. They suit high speed digital boards and mixed analogue and digital designs where the loss budget is tight but a full PTFE process is not justified.
Polyimide laminates. High glass transition temperature and a very wide operating range, used where the board has to survive extreme thermal cycling, in aerospace, defence and some industrial applications. They are mechanically tough and thermally stable, at a higher cost and a higher moisture uptake than the low loss materials.
Thermally conductive dielectrics. Thin, filled dielectric layers on a metal base, used to move heat out of power devices and LED modules. The dielectric has a defined thermal conductivity and a dielectric strength, and the construction is a metal core board rather than a conventional laminate.
Properties That Decide the Choice
Dielectric constant. It sets the trace geometry for a given impedance and, where it varies with frequency or from batch to batch, it sets the tolerance on the impedance. A low and stable value is what makes a wide band RF circuit predictable.
Loss tangent. The dielectric part of the insertion loss, and the property that most often justifies a premium material. It matters for a long trace, a high frequency or a narrow link budget, and it matters little for a short, slow signal.
Glass transition and decomposition temperature. The thermal margin through lead free assembly and through the multiple lamination cycles of a multilayer or HDI build.
Coefficient of thermal expansion. It determines the strain on the plated holes and on the surface mount joints as the board heats and cools, and it matters most in a product with a wide operating range.
Moisture absorption. A low value keeps the electrical properties stable in a humid environment, reduces delamination during assembly and lowers the risk of conductive filament growth between the conductors under bias.
Thermal conductivity. The property that makes the thermally conductive grades useful, and the one to look at first when the problem is a hot device rather than a fast signal.
Mechanical strength and dimensional stability. A PTFE laminate is soft and will move under stress, so a design that requires a tight mechanical tolerance or a fine pitch overlay has to account for it.
Processing These Materials
The processing differences are what make a high performance laminate more expensive than its material cost suggests. A PTFE based board is soft, so it needs sharper drills, a different drill parameter set and a controlled entry and exit material, and it responds to heat differently from FR-4. Its surface is chemically inert, so a plated hole or a bonded coverlayer requires a surface preparation step, such as a sodium etch or a plasma treatment, that an FR-4 process does not.
Thermoset low loss laminates are closer to FR-4 and can often run on the same line with modified parameters, which is why they are frequently the practical answer for a high speed digital board. Polyimide laminates are hygroscopic and have to be baked before lamination and before reflow, or the trapped moisture will delaminate the stack. Thermally conductive metal core boards use a different process again, because the base is aluminium or copper and the dielectric is laminated or coated onto it rather than being a conventional core.
In all cases the surface finish, the solder mask and the final coating have to be compatible with the material and with the assembly process, and the finish change can affect the high frequency performance of a fine line circuit. Our notes on PCB manufacturing describe how these processes are controlled.
Common Difficulties
Warp and dimensional movement. A laminate with a low glass transition temperature or a high coefficient of thermal expansion moves during lamination and during assembly, so a stack that is not balanced will bow and a design that assumes FR-4 stability will not fit its enclosure. The stack-up should be symmetrical and the material supplier’s data should be used rather than an assumption.
Copper adhesion. The chemically inert surface of a PTFE laminate makes copper adhesion harder, and the plating and the bonding steps have to be matched to the material. A poorly prepared surface produces a plated hole that pulls away or a trace that lifts.
Impedance control. A high frequency board is usually specified with a tight impedance tolerance, and that tolerance depends on the dielectric constant, the dielectric thickness and the trace width. The design and the fabricator’s stack-up have to be worked out together, because a field solver used with the wrong dielectric thickness produces a confident and incorrect answer.
Mixed material stacks. Using a high performance material only on the signal layers and a standard material elsewhere is a good way to control cost, but the lamination cycles, the thermal expansion and the drilling parameters of the two materials have to be compatible, and the interface between them has to be designed rather than assumed.
Our notes on PCB design and layout cover how these constraints are translated into a stack-up.
Where These Materials Are Used
Aerospace and defence electronics use them for radar, electronic warfare, satellite communication and avionics, where the combination of high frequency performance and thermal reliability is difficult to obtain from a standard laminate. High frequency communications use them in antennas, filters, couplers and the front end of base station and microwave radio equipment.
Automotive radar and sensor modules use them where the microwave performance has to hold across the temperature range of a vehicle, and LED lighting and power modules use the thermally conductive grades to move heat out of an LED array or a power stage. Industrial control and instrumentation use them where a low loss, stable material makes a measurement repeatable.
Cost and Selection
A high performance laminate costs several times more than standard FR-4 per unit area, and the process adds more, because the yields are lower and the equipment and chemistry differ. The right way to evaluate it is against the cost of the alternative: a redesign after a failed first article, an additional layer to compensate for loss, a retimer on a faster interface, or a heatsink that would not be needed if the board conducted heat better.
The selection itself follows from the requirement rather than the material name. Start with the frequency and the loss budget, then the thermal environment, then the mechanical and environmental requirements, and let those three narrow the options. Confirm the choice with the fabricator before the layout is released, because the dielectric constant that matters is the one the stack will actually have. Our notes on PCBA testing describe how the finished board is verified, and our notes on quality management cover how the material and the process are controlled.
FAQ
Is Arlon a single material? No. It is a family of laminates that includes PTFE based RF materials, low loss thermoset materials, polyimide materials and thermally conductive dielectrics, each for a different requirement.
Will it work with a normal FR-4 process? Thermoset low loss grades often will, with parameter changes. PTFE based and metal core materials need a different process, including surface preparation before plating.
Can I mix it with FR-4 in one board? Yes, and it is a common cost control measure, but the stack has to be balanced and the process parameters of both materials have to be compatible.
Why is impedance control harder on these materials? Because the dielectric constant and the dielectric thickness have to be known precisely, and the tolerance on both is what sets the impedance tolerance rather than the trace width alone.
When is a thermally conductive grade the right choice? When the limiting factor is the temperature of a power device or an LED rather than the speed or the loss of the signal.
Conclusion
Arlon PCB materials are a set of solutions rather than one product, and the selection is straightforward once the problem is stated clearly. PTFE based grades for low loss radio frequency circuits, low loss thermosets for fast digital designs, polyimide for extreme thermal cycling and thermally conductive dielectrics for heat. Each carries a processing penalty that has to be planned for, and each is worth its cost only when it solves the requirement that a standard laminate cannot.
