Gauss Stack Frequently Asked Questions

What is "Trap Ratio"? How does this relate to etch factor and angle?

The "trap ratio" that we ask for in synthesis mode merely refers to the ratio between the width at the top of the trace conductor and the width at the bottom of the trace conductor. This is a much simpler and more direct number than the etch factor and angle. The conversion between our "trap ratio" and the etch factor and angle are as follows:

I want to add a material to my Materials Library, but I'm a bit unclear on what properties to input in Materials Entry? Can you provide some guidance?

Firstly, all of the properties to be input in Materials Entry pertain to the neat resin. Please see below for a detailed explanation of each property and what you need to provide for each entry.

 

Name: This can be any combination of letters, numbers, and symbols.

Modulus: The elastic modulus of a material is defined as the slope of the stress versus strain in the linear portion of the stress strain curve. A material with high modulus will be stiffer and offer more resistance to elastic deformation. The value to be filled in this column is the Young’s Modulus (in GPa) for the neat resin (including fillers and other additives).

A typical unfilled epoxy resin may have a Young's Modulus of ~3-4 GPa, but may be as high as ~7-8 GPa for a highly filled resin system, though, most often, this is ~4.5-6 GPa for standard filled systems. A thermoplastic will typically have a lower Young's Modulus of ~1-4 GPa.

 

Density: The density of a resin typically varies between 1.2  g/cm^3 (non-brominated systems) to >1.7 g/cm^3, depending on the level of fillers. Most commonly, the density will be between 1.3 - 1.55 g/cm^3.

Poisson Ratio: The Poisson ratio is a negative ratio of the transverse to longitudinal strain. This value for a material can vary between 0 and 0.5. The value to be inserted is the value for the resin including fillers and additives. This value is typically around .35.

CTE: This is the linear coefficient of thermal expansion of the neat resin itself in parts per million per degree C (PPM/C). Values will typically range from 30-70 PPM/C. Unfilled epoxy resins are close to 65 PPM/C.

Tg: This is the glass transition temperature of the resin itself (in degrees Celsius). The glass transition temperature required for Gauss Stack's computations is the TMA (Thermo-Mechanical Analyzer) Tg. The TMA Tg measures the inflection point on the expansion vs the temperature slope and is, thus, the relevant temperature for our computation. TMA Tg values tend to be lower than the DSC (Differential Scanning Calorimetry) and DMA (Dynamical Mechanical Analyzer) Tg values.

Flow Factor: This is an empirical factor that is used to calculate the flow from the PCB stack-up package. Typically between 0.005 and 0.025 of the resin will leave the package, depending on how fluid the resin is at higher temperatures and what kind of temperature, time, and pressure history it is being subjected to. Typically, a flow factor of between 0.005 and 0.01 is a good representation of the physics if the resin shows normal flow behavior. If this input is not provided, Gauss Stack will assume an idealized case of 0 as the flow factor.

 

Lamination Temperature: This is the highest temperature, in degrees Celsius, that that material is exposed to in the lamination cycle.

 

Bonding Temperature: This is the temperature (in degrees Celsius) at which the resin turns to solid state and also represents the stress-free temperature. This is heavily influenced by the rate of rise (temperature vs time ramp) and the viscosity of the resin as a function of temperature and the rate of rise. Your material supplier can provide this information by simulating the press cycle conditions on a rheometer and identifying the gelation (solidification) point. 

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