MEGTRON 6 – High Speed, Low Loss, Multi-layer PCB Material
Deciding on the right laminate material for a PCB is very important. For most rigid and rigid-flex laminates, you can go with the age-old option of FR-4 material. It’s cheap, mechanically stable, and it makes fabricating multilayered PCBs easy.
But the problem with FR-4 is that at high-frequency and high-speed applications, it’s a very loss-prone material. So in high-speed, high-frequency applications where signal integrity is a major consideration, you have to look at the alternatives. One good option for low-loss applications is PTFE. It shows amazing results and electrical characteristics in high-frequency and microwave circuits. But it fails to meet the stability requirements of a multilayer circuit. At higher temperatures, its dielectric quickly falls below the desired threshold, and its dimensional stability is compromised. It can be used in conjunction with polyimide for better mechanical characteristics.
But one of the best and most commonly used High-speed and low-loss material for multilayer PCBs have been Megtron 6.
Megtron 6 is Panasonic’s high-speed, low-loss laminate system that’s been around for well over a decade. The material was specifically designed to cope with the high-speed network equipment demand of the market. The high signal losses in the FR-4 had turned the market away from this most common PCB laminate. And compared to other high-speed low-loss materials, Megtron 6 was (and still is) one of the most affordable and mechanically stable laminate material.
At the time of its introduction, this woven-glass reinforced laminate system had the best combined-performance specs in the industry. It’s still one of the top choices for low loss materials. And it’s very cost-effective compared to relevant materials like Rogers 4350B.
Some of the most common applications of Megtron 6 are Different Antenna types, Mainframes, supercomputers, high-precision instrumentation, and ICT applications. IBM has been using Megtron 6 for over their mainframe series (Z) for over a decade.
Megtron 6 is also becoming the laminate material of choice for high layer-count HDI circuits.
Megtron 6 Specifications and Stats
Usually, a laminate’s thermal, mechanical, electrical, and chemical properties are all important factors in choosing the right laminate. For this article, we will take a look at Megtron 6’s electrical and mechanical characteristics.
At low-frequency end of the gigahertz frequency applications (at 1 GHz), Megtron 6 offers amazing electrical characteristics:
Dielectric constant (Dk): 3.7 (A low dielectric constant promote high-frequency transmission)
Dissipation factor (Df): 0.002 (In high-frequency applications, designers tend to look for the magic number of 0.003 or lower)
Even if we consider the higher frequency electrical characteristics of Megtron 6, the numbers are still impressive. At 12 GHz, the constants are:
Dielectric constant (Dk): 3.35
Dissipation factor (Df): 0.04
A good dissipation factor (or a low loss tangent) requirement is usually a major consideration in analog circuits, where signal losses cannot be tolerated, degree of attenuation and maintaining a healthy signal to noise ratio is imperative.
In terms of the dissipation factor, Megtron 6 falls short only of the super low-loss materials with dissipation factors of 0.001.
Volume and surface resistivity values of Megtron 6 are 1 x 10^9 MΩ – cm and 1×10^9 MΩ, respectively.
Megtron 6’s FR-4-like mechanical and superior thermal characteristics, make it ideal for multilayer applications. Since multilayer fabrication means multiple lamination cycles, a high decomposition temperature is desirable.
Megtron 6’s basic thermal stats are:
Glass transition temperature (Tg): 185-210 °C (based on DSC and DMA testing method, respectively).
Thermal Decomposition Temp (Td): 410 °C (Based on TGA testing method)
Z-axis thermal expansion: 45 ppm / C (within Tg) and 260 ppm / C (for temperatures above Tg)
The high heat resistivity values of Megtron 6 make it ideal for multilayer fabrication. It gives the freedom of mechanical design like FR-4, coupled with the low-loss characteristics of comparatively expensive materials.
A Wide Range of Options
Megtron 6 offers a wide variety of laminate thickness and prepregs. There are 18 choices for laminate thickness and 11 different glass styles for different prepreg constructions. This allows you to tweak the mechanical, chemical, and thermal attributes of your laminate to make it a perfect fit for your application within your budget.
Another great attribute of Megtron 6 is the resin coating. Unlike other woven-glass reinforced laminates in the same price range, Megtron 6 is made with microscopic perfection. The resin is evenly coated on the surface of those tight weaves. And you have the option of choosing among one of the three resin content percentages.
It is also important to note that few laminate materials in the market offer such a wide range of construction options.
Perfect for Multilayer PCBs
With electrical characteristics nearly similar to those of higher-price, high-speed and low loss materials, and mechanical and thermal characteristics of FR-4, with a very high dimensional stability, Megtron 6 is an amazing choice for multilayer PCBs and HDI applications. Unlike other such materials that can only be employed for cap constructions, Megtron 6 is well suited to foil construction.
Since it can go through a lot of lamination layer without any structural damage, it also allows for complicated HDI constructions (Type III and other stack-ups with buried, stacked and staggered vias).
It also has fantastic through-hole reliability, many times better than an FR-4 laminate in the same Tg range. Since it also allows for lead-free, ROHS-compliant soldering, it is the laminate of choice for many complicated high-speed circuit constructions, and compatible with a wide array of components.
For your high-speed, low-loss circuit design, Megtron 6 can be a fantastic choice, even if you are working with just a few layers and can design with cap construction. It’s very cost-effective, with electrical characteristics just slightly lower than much costlier laminate materials at frequencies higher than 5 GHz. For multilayer applications, Megtron 6 is one of the few good choices. Before you start designing, make sure you know which materials are available to your fabricators, and whether they have the capabilities of tweaking there assemble line for a certain material.
This is another area where Megtron 6 shines as a laminate; it doesn’t require any assembly line parameter changes from FR-4.