Avishtech announced significant enhancements to its Gauss Stack PCB stack-up design and simulation toolset that enable the most accurate prediction and specification possible of the maximum fiber-weave related skew on differential pairs. For today’s high frequency, high data rate products, the ability to predict, specify and fine tune a design such that it is not impacted by glass weave-induced skew becomes a critical factor at the stackup design stage of the product development process.

Glass weave-induced skew in differential pairs is caused when a trace runs over a glass fiber for some distance and then between glass fibers. When this happens, the dielectric constant varies substantially, causing significant variations in impedance and velocity along the trace. When the two members of a differential pair travel over the weave pattern these variations may not be equal in both members. This results in skew between the two sides of the pair and degradation of the signal at the receiver.

Keshav Amla, Founder and CEO of Avishtech, notes, “In recent years there have been some approaches developed within the industry to address skew. One approach involves using multiple plies of the glass cloth to reduce the likelihood of perfect alignment while another involves mechanically spreading the glass within the cloth to achieve uniformity of the weave. Beyond this, designers focused on mitigating skew are more often using low Dk glass and also rotation of the traces.  Often, designers will be using a combination of these and trying to match the widths and spacings to the pitch of the glass, but this technique, rotation and the multiple plies approach may not work for applications focused on increased routing densities. Rotation can also lead to resonance, which can lead to additional insertion loss. More importantly, until this iteration of Gauss Stack, there has been no way to predict and accommodate weave-induced skew at the stackup phase of the PCB design process – every stackup and every differential pair on each stackup will behave differently with regard to skew. Without this capability, you can end up with one of the hidden ‘gotchas’ that can turn your working high frequency, high data rate design into a failed PCB before you have even gotten to the manufacturing process.”

“Avishtech’s Gauss PCB Stackup Designer and Simulator is a game-changer in characterizing and predicting glass weave induced skew,” said Scott McMorrow, Strategic Technologist at Samtec, Inc. “When evaluated against Samtec’s real world skew measurements and skew mitigation trace designs, Gauss Stack successfully matched our expectations and data. Designers can leverage this unique tool to test design aspects of various laminates and trace geometries to help achieve desired results. I would recommend that anyone interested in differential pair skew look into this innovation.”

Note: Avishtech will be exhibiting at DesignCon, booth 521. Those interested in learning more about our toolsets or getting a demo is welcome to stop by at the show!

The specific steps within Gauss Stack that address skew include:

  • Specifying the materials and constructions within the stackup.
  • Selecting the copper layer.
  • Specifying the trace width/gap and orientation of the trace relative to the warp and weft directions of the glass weave.

Once the foregoing operations are completed, the product developer clicks a button to do a stochastic Monte Carlo simulation (which is variable and random due to the weave of the fiber) to build a distribution and confidence intervals for the maximum skew on the design’s differential pair. This means that product developers can simulate and design for skew at the stackup design stage to find something that works specifically for their design and have a high level of trust that the information they have at this step of the design process is going to be right for the manufacturability, operability and long-term reliability of the product.

“In some applications, there might be the need for additional skew mitigation approaches such as rotation and/or retimers,” Amla notes, “but the key thing is that designers will be able to predict skew and find what is going to work out the gate or gets as close as is possible with a high level of confidence that the end-product will work as designed. This eliminates the large amounts of time and high NRE costs, not to mention the impracticality, associated with having to build and measure hundreds of differential pairs for each new design. Being able to characterize skew at the stackup stage of the design means that your design will work right the first time, maximizing the life and profitability of the product.”

Product Availability and Delivery

Gauss Stack with its enhanced skew characterization and prediction capabilities is available now. Instead of the traditional pricing methodologies of a toolset license per seat, Avishtech utilizes a subscription-based customer fulfillment model. Each year, an Avishtech customer buys an annual subscription, based on their design needs criteria, and all the enhancements, additions and technology advancements made to the product during that subscription period are included in the subscription price. System software requirements include: OS Microsoft Windows 10 (64 bit); Recommended CPU—64-bit Intel i7 Quad Core processor running at 4.0 GHz or better (Requirement: 64-bit Intel Dual core processor running at 3.0 GHz); Recommended memory—16 GB or higher (Requirement 8 GB or higher).