Keywords: RF Microwave PCB

This is the reason why over the past several years we have had to invest in Microwave & RF Printed Circuit Boards so that we could expand our manufacturing capabilities and become a global producer of high frequency laminates. RF and microwave PCB have elements that convey RF or microwave signals.

By and large, these applications demand laminates that have electrical, thermal, mechanical or other performance profiles that go beyond the simple standard FR-4 features. Due to our extensive experience in manufacturing PTFE-based microwave laminate we know that most of the application demands high reliability as well as low tolerance.

Hybrid PCB is the special category of RF & microwave PCBs that use both FR-4 and PTFE or any other material inside the stack up.

PCB Material Stock

Will all the different features of every RF PCB application, we have formed strategic relations with major material suppliers like Rogers, Arlon, Nelco, Taconic and many other. Most of the stocks are specialized nevertheless; we do have fairly good stocks of product in our ware houses from Rogers (4003 & 4350 series), Arlon etc. Few organisations are willing to do that because the cost of holding inventory to enable a quick response is usually very expensive.

High frequency laminates used for fabricating high technology circuit boards makes the design process of such circuit boards complicated due the sensitivity of the signals and the issues related to heat transfer in most applications. Optimum high-frequency PCB materials display low thermal conductivity as compared with the FR-4 material incorporated in the conventional PCBs.

RF & microwave signals are extremely noisy sensitive, and have higher impedance requirements than conventional digital circuit boards. The ground plans and generous bend radius on impedance controlled traces must be employed to have the design operate in the best possible manner. Almost all PCB assemblers and manufacturers currently offer standard PCBs deployed in many electronics products. But all of them may not possess the capacity to prepare RF and microwave PCBs. Expanded interest in electronic devices and new developments have added to extensive progress in these PCBs.

As wavelength of a circuit depends on its frequency and on material the RF microwave PCB materials with higher dielectric constant (Dk) values can lead to smallest PCB as miniaturized circuit designs for specific impedance and certain frequency ranges can be used. In most cases, to gain higher Dk, laminates of Dk of 6 or more are used in conjunction with lower cost FR-4 materials in multilayer structures.

Knowing the CTE, dielectric constant, thermal coefficient, TCDK, DF, and even items like relative permittivity and loss tangent of the available PCB materials will assist the RF PCB designer in developing a design that meets and possibly goes beyond the desired characteristics.

Before final decisions about the type of substrates to be used certain other factors need to be decided and some of them include the following line width for a range of board thickness which may be left for final determination after the circuit working frequency has been established as well a s the approximate dimensions of the leading components.

Different RF PCB material types are:

Polytetrafluorethylene (PTFE) reinforced with ceramic, which demonstrate great electrical and mechanical stability. Rogers RO3000 series circuit materials have good mechanical property and there is no change over dielectric constant (Dk), which means multi-layer board design employing different dielectric constant materials would not experience war-page or reliability issues. Taconic RF series of products has low dissipation factor & high thermal conductivity possible so it will not oxidize, yellow or show upward drift in dielectric constant & dissipation factor like its competitors based on hydrocarbon.

Megtron 6 circuit board material – Ultra-low loss, highly heat-resistant & halogen free component. High TG and the minimum expansion ratio of hydrocarbon resin based MEGTRON 6 – makes it the choice material’ for High Density Interconnect (HDI) and high speed (above 3 GHz).

Woven glass reinforced PTFE laminates are made from very light weight woven fiberglass and are even more dimensionally stable than chopped fiber reinforced PTFE composites. The dissipation factor or the loss factor is rightfully low in such materials such as Taconic TL family of materials; thus, it is ideal for radar applications designed for 77 GHz, and other antennas in millimeter wave frequencies.

Hydrocarbon ceramic laminates are used in microwave and millimeter-wave frequency designs as this low loss material facilitates easier use in circuit fabrication and streamlined properties compared to other PTFE materials. Rogers RO4000 series of products are available in a broad range of dielectric constant (2.55-6.15) and have average to high thermal conductivity (.6-.8).

There exist laminates of PTFE-filled with glass or ceramics such as the Rogers RT / duroid high frequency circuit materials that possess low electrical loss, low moisture absorption, and low outgassing suitable for space usage.

Thermoset microwave laminates incorporate low TCDR, a copper matched coefficient of thermal expansion and good mechanical endurance. The Rogers TMMs are high frequency laminates, special suitable for reliability strip line and micro strip circuits.

Specialized Processing Equipment

Most of the microwave/RF PCB processing are similar to that of the standard fabrication equipment. However, design solutions of the greatest complexity presuppose the use of specialized equipment. We have invested significantly so that we have in-house: Plasma Etch equipment is used so that the quality of the thru-holes is high so that it can withstand the requirement of drilling the advanced technology to pass through it. In plasma etching, through holes and other surfaces of the substrate will be etched using plasmas or etchant gases to make room of the subsequent coating. LDI equipment against the more traditional photo exposure tools so that we can achieve very tighter trace widths and front to back registration. Laser drill equipment required for many of the various materials as mechanical cutting will leave burr, unlax fabric or even turn color due to heat. This also helps us ensure that we so provide customers with microvias of the best quality in every order that they place to us.

Standard procedures of RF and Microwave PCB Assembly

Almost all PCB assemblers and manufacturers currently offer standard PCBs deployed in many electronics products. But all of them may not possess the capacity to prepare RF and microwave PCBs. Expanded interest in electronic devices and new developments have added to extensive progress in these PCBs. The following is a list of a few of the important considerations that are given out when making these PCBs.

RF microwave PCB is manufactured by the use of quality materials such as high FR4, ceramic-filled hydrocarbon, amongst others. These materials are popular because they are quite thick and can be easily bent in numerous forms. These have a desirable coefficient of thermal expansion (CTE) specification. These materials help in providing stable board structure whose functionality is enhanced in extreme conditions.

Material used in RF and microwave PCBs must guarantee the performance of the board in all types of adverse conditions.

HT materials mean that high layer counts are feasible, including very fine geometries and detailed patterns.

Laser equipment is also incorporated in these boards for imaging besides use in the acquisition of narrow tracing width.