In this article, you will learn about Sierra’s 3 free HDI tools, essential for HDI PCB design. We will present and explain how our HDI Stackup Planner, our HDI Material Selector, and our Impedance Calculator work so you can choose which one best suits your needs.

Since it was developed at the end of the 20th century, HDI technology – which stands for High Density Interconnection – is very popular. HDI technology transformed our electronic products. We now have smaller, lighter, and faster products such as cell phones and computers.

Unlike traditional PCBs, HDI boards can obtain interconnections through blind vias, buried vias, and microvias, instead of just through holes with via-in-pad, which means that microvias are located directly in the solder pads.

Manufacturers only use laser drilling on these boards to get apertures and line widths as thin as 3 mil. This precision drastically shrinks the pad size: therefore, HDI boards support more connections on fewer layers.

Designers can now place more components on each side of their circuit boards. But placing smaller components closer together is not as easy as it seems. This is why Sierra Circuits has developed free HDI tools for better PCB design.

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HDI Stackup Planner

Sierra’s free HDI Stackup Planner helps you make sure that your HDI PCB design can be manufactured the very first time without any issues.

This tool asks you to fill out your board information, like the part number, the revision number, the PCB estimated size, and the finished thickness. Because we know it is not simple to choose the exact thickness, we came up with a solution: you can simply pick an estimated thickness and the stack-up tool will create a PCB stack-up that meets your needs.

You can now select the material that will best suit your design needs among a list of 12 materials provided by Sierra. The stack-up gives you the type, the typical application areas, the glass transition temperature (Tg), the dielectric constant (Dk) values, the dissipation factor (Df) values, the electrical strength, and the cost factor for each material.

Your stack-up design is the third step. Mention whether the outer layers of your final stack-up will be signal or plane. The tool then gives you multiple choices, depending on your answers, which lead to the stack-up options table with parameters such as the number of layers, the sequential laminations, the PCB thickness, the cost index, etc.

If you need to, you can run the Impedance Calculator as shown below in this article.

HDI Material Selector

How to use Sierra’s Material Selector

Just like the HDI Stackup Planner, our free HDI Material Selector requires you to fill out your HDI board information as best as you can. Note that if you cannot provide all the information, the tool will still give you matching materials suitable to your application.

First, answer whether high speed applications and / or lead free PCB assembly apply to your board or not.

You can choose your IPC number, and the slash number that completes it.

IPC-4101: Specification for base materials for rigid and multilayer boards

IPC-4103: Specification for base material for high speed / high frequency applications

IPC-4104: Specification for high density interconnect (HDI) and microvia materials

IPC-4204: Specification for flexible metal-clad dielectrics for use in fabrication of flexible printed circuitry

The slash number is an appendage to the standard that specifies what a system of resin and fiber material has to comply with in order to meet the conformance. It is specified for both prepreg and base material in the slash-sheet.

When it comes to the material characteristics, mention if your laminate material is CAF resistant. This refers to the Conductive Anodic Filament growth, “a form of electrochemical migration within a printed wiring board,” as described by IPC. CAF is a failure mode in PCBs that occurs under conditions of high humidity and high voltage gradients.

You can select a range for the glass transition temperature in degrees Celsius (TgoC). This is an important normative dimension for the base material that determines the temperature at which the resin matrix converts from a glassy, rigid state to a softened, deformable one. We allow a range from 130oC to 280oC. The standard Tg for copper clad laminate is between 130 oC and 140 oC, whereas High Tg (PCBs with higher heat resistance used for high reliable products) is generally greater than 170 oC.

The dielectric constant (Er or Dk) of a material is important for signal integrity and impedance considerations. Sierra offers a dielectric constant range from 2.17 to 10.20, but most PCB materials range from 2.5 to 4.5. The dielectric constant varies with frequency: generally, as frequency increases, the dielectric constant decreases. The dielectric constant of materials suitable for high frequency applications remains relatively the same over a wide frequency range – from 100MHz to several GHz.

The dielectric loss tangent (Tan δ) – also called the dissipation factor – gives a measure of power lost due to the material. We give you a range from 0.0005 (for very low-loss high-end materials) to 0.0230 (for most commonly used materials). Keep in mind that the lower a material’s loss tangent, the less power loss. Loss tangent is a very important parameter for analog signals: it determines the degree of signal attenuation, which affects the signal to noise ratio at various points along signal traces. Under 1GHz, loss tangent is usually not a critical consideration for digital circuitry.

If you already know which material you want, you can select the family name:

– FR-4 (glass-reinforced epoxy laminate PCBs)

– Polyimide (best for the production of rigid-flex and flex PCBs)

– Teflon

– Ceramic

– Cyanate Ester

– Bond Sheet / Special Dielectric (prepreg) materials

– Flex

– Resistor

– Thermal

And if you also know which material manufacturer you want, choose among:

– Arlon

– Dupont

– Isola

– ITEQ

– Laird

– Nan Ya

– Nelco

– Ohmega

– Panasonic

– Rogers

– Taconic

– Thermagon

You can now click the “Find Materials” button.

For instance, if you want a lead free assembly, IPC-4101, CAF resistant board, here is what the HDI Material Selector gives you:

All that is left to do is choose, and compare materials side by side.

Impedance Calculator

Controlled impedance measures in Ohms (Ω) the resistance applied to an electrical current traveling through a circuit. It is essential for signal integrity: signals have to get from one component to another at a certain time to be as clean as possible. Failure to do so would cause electromagnetic interference.

At high signal speeds, the signal traces of a PCB act like transmission lines. Having a controlled impedance – also called characteristic impedance – at each point on the signal trace maintains the signal integrity. If this impedance varies from one point to the next one, there will be a signal reflection whose magnitude will depend on the difference between two impedances. The bigger the difference is, the greater the reflection will be. This reflection will travel in the opposite direction of the signal, which means that the reflection will superimpose on the main signal. As a result, the original signal will be distorted.

The distortion may be so much that the signal may not be able to operate at the desired function. Therefore, to have an undistorted signal travel, it is essential that the transmission line or the signal trace has a uniform controlled impedance.

If you maintain the geometrical uniformity of the signal traces – same height and width all along the traces with a +/- 10% tolerance – they will act as uniform transmission lines and their impedances will be uniform.

How to use Sierra’s Impedance Calculator

The first thing to do is to choose what kind of impedance you want: single-ended or differential.

For single-ended impedance, you can see:

– The dielectric height

– The dielectric constant

– The trace width

– The trace thickness

– The SE impedance

– The propagation delay

– The inductance

– The capacitance

Enter the SE impedance you want, the trace width, and the trace thickness (if not already pre-filled) and click the “Calculate Impedance” or “Calculate Trace” buttons.

For differential impedance, you can see:

– The dielectric height

– The dielectric constant

– The trace width

– The trace separation

– The trace thickness

– The differential impedance

– The odd mode impedance

– The even mode impedance

– The common mode impedance

– The propagation delay

– The inductance

– The capacitance

Enter the differential impedance you want, the trace width, and click the “Calculate Impedance” or “Calculate Trace” buttons.

Note that, in both cases, Sierra’s stack-up team does not check the odd mode impedance, the even mode impedance, the propagation delay, the inductance, and the capacitance because most boards only require one or sometimes two types of impedance: single-ended and differential.

For more information on HDI PCB manufacturing, visit our website.

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