E-NEWSLETTER l MAY 2021
A MESSAGE FROM OUR CEO
One of the things we are proud of at ASC is the leadership role we have taken when it comes to the PCB RF Market. Some people like to say we were in this market before it was “cool” (Pun Intended). For twenty years we have been producing RF boards, from the early days of overcoming the difficulties of laminating Teflon materials, something that one of our engineers described as trying to get two fried eggs to stick together, to today where we deal with specialized RF materials in our RF microwave boards. We have extended our offerings to include metal-backed boards and have in-house milling equipment to produce our own milled metal materials.

Now with the onset of 5G, we are at the cutting edge of this technology and properly poised to handle all the technological challenges working in the RF space brings.

In this edition of our Technical newsletter, you’ll find valuable material about RF technology and our own abilities to handle all our customers’ RF needs.

And if you have not done so yet please download our series of Technical Books, including our new THERMAL MANAGEMENT: A FABRICATOR’S PERSPECTIVE. Remember we’ve written the book on Thermal Management!

As always thank you for your business and most importantly the trust you have invested in ASC by allowing us to help build your products of the future.

Sincerely,

Anaya Vardya
President and CEO
American Standard Circuits
Cavity Construction

Cavity PCBs have structural recesses to enable additional functionality compared to a standard Printed Circuit Board. This type of feature allows the insertion of heatsinks, often referred to as “coins”, or used to position electronic components below the surface, thereby giving the assembled PCB a thinner overall profile. The inner cavity surfaces can also be used for electrical contact, normally a ground connection. While there are many ways to create a cavity in a PCB, the most common method is by mechanically removing material from a PCB structure to create a “window-type” cavity in a multilayer PCB. As the laminate and prepreg layers are assembled, the layers forming the windows will create the walls of the soon-to-be cavity. If the cavity is functioning as a RF/microwave resonant cavity, the frequency is determined by the size of the cavity and the PCB manufacturer must tightly control the X, Y & Z dimensions of the cavity. Cavity designs can be applied in multiple locations and different depths on a single printed circuit board and can also be edge plated.
Cavity Construction.

Prepreg Materials
Prepreg is a shorthand expression for "PRE-imPREGnated"; a fiberglass or other fabric reinforcement which has been saturated with a partially cured resin system at the laminate manufacturer. Prepreg is also called B-Stage or Bonding Sheet. When the prepreg is laminated (bonded) in the multilayer package at the PCB manufacturer, the prepreg “flows” under heat and pressure. In a standard multilayer construction, prepregs with “high-flow” characteristics are desired to ensure encapsulation of circuits, filling of holes and elimination of voids. But when bonding cavity PCBs, a “no/low-flow” prepreg is preferred. It is important for designers to understand that even no/low-flow prepregs flow, but the flow can be more controllable and predictable. That being said, it is also important to recognize that the flow characteristics are impacted by the underlying PCB circuit/plane pattern and the configuration of the bonded heat sink.

To compensate for the flow, the PCB manufacturer will engineer the prepreg route program to recess all the edges, so that after lamination the prepreg flows back to the desired position.
Low Flow Prepreg Cutback.
Each no/low-flow prepreg has a unique resin flow percent tolerance which needs to factor into this adjustment. However, even with the best flow characteristic modeling, some trial-and-error lamination cycles may need to be run before the bonding profile can be finalized. Another critical consideration is that some flow bleed into the cavity is desired to assure complete bonding. By collaborating with the PCB manufacturer, RF designers can avoid selecting bonding materials that lack good flow control and might flow into the resonant window or cavity area. In a resonant cavity design, changing the dimensions of the resonant cavity will change its operating frequency.

Cavity Design Considerations
·        Cavity designs should utilize no/low-flow prepreg
·        Acceptable bleed into cavity needs to be defined; IPC 6018 allows .029”
·        Critical Registration: special tooling, fixturing and bonding profiles are required
77 second webinar on Cavity Construction
UPCOMING WEBINARS
Rogers- Adhesive and Bonding Material Options for High Frequency
May 26, 2021
11:00 am to 12:00 pm (CDT)

The focus of this presentation will be on the adhesive and bonding material options for high frequency printed circuit designs. We will examine the electrical, mechanical, and thermal performance parameters which all need to be factored into final adhesive choice.
Design Guidelines associated with Unique RF Features
June 16, 2021
11:00 am to 12:00 pm (CDT)

Many RF boards have cavities and/or edge plating. Cavity PCB’s have structural recesses to enable additional functionality and can be seen in a number of different RF applications. These types of features allow insertions of heat sinks. The inner cavity surface can also be used for electrical contact, normally a ground connection. Edge plating may be required to improve EMI shielding and/or improve chasis ground in electronic systems. This webinar will discuss various design considerations associated with these specific features.
ON DEMAND RF WEBINARS!
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DOWNLOAD OUR RF/MICROWAVE EBOOK!
Today’s designers are challenged more than ever with the task of finding the optimal balance between cost and performance when designing radio frequency/microwave PCBs.

Readers, especially RF PCB designers, will gain a better understanding of issues related to the design and manufacture of RF/microwave devices from a PCB fabricator perspective.
Our Experts are one reason why American Standard Circuits is North America's leading independent PCB fabricator. Our entire experienced and professional staff is ready and able to make your next PCB project easy!