Using Sierra Circuits‘ free HDI Stackup Planner before you begin your layout design will ensure that your HDI PCB design will be manufacturable the very first time.
Step 1: The Board Information
The first thing you have to do to use this tool is to fill out the board information. Fill out a part number, like Sierra Test for example; a revision number, like 2; the estimated size of the PCB, like 4 inches by 4 inches; and then choose the finished thickness – you don’t have to choose an exact thickness, the HDI Stackup Planner will try to find a thickness that comes close enough – like 0.062 inches, in this case.
Step 2: The Material Selection
In order to help you determine what sort of material will best suit your design needs, Sierra provides a list of 12 materials, with their most important properties, that you can compare. We chose these specific materials out of a whole list of PCB materials because they are suitable for HDI PCB manufacturing, and they almost cover the entire range of HDI applications.
For each material, you can see:
– The type
– The typical application areas
– The glass transition temperature (Tg)
– The dielectric constant (Dk) values
– The dissipation factor (Df) values
– The electrical strength
– The cost factor
We provide the cost factor to give you an idea of the relative cost of each material.
After selecting a material, you can click the “View” button to see a lot more characteristics from the data sheets.
Step 3: The Stackup Design
Now that you have chosen the material, you can start the Stackup design. The first key design question is whether the outer layers of your final Stackup will be signal or plane. Almost every electrical engineer knows what the answer would be depending on their application and constraints.
If you have signal on the outer layers, the HDI Stackup Planner gives you two choices: run the tool based on specifications of your most complex BGA in your design, or you can select the layers based workflow if you already know how many signal layers you need in your design.
- If you have a complex BGA in your design that will generally drive the stack up design…
You can select the number of pins in X1 direction and Y1 direction, enter the BGA Pitch, the total number of pins, and the estimated number of signal pins.
- If you have a fairly good idea of the number of signal layers required in the design…
You can select the number of layers, like 10 for instance. The tool then asks you to select the number of signal plane combinations, like 6 signals and 4 planes. This is all you need to provide to run the HDI Stackup Planner.
The tool now gives you a table of Stackup options. In this case, there are 6 options – from Option A to Option F.
If you look at Option A, you have 6 signal layers and 4 plane layers for a total of 10 layers, exactly as we wanted. It is a standard construction – not HDI – so it has 0 sequential laminations. The PCB thickness is 0.062 inches. You can see a series of columns under “Cost Index” for different technology levels. In the last column, the tool provides a detailed report.
If you look at Option D, you have again 6 signal layers and 4 plane layers for a total of 10 layers. This is an HDI Stackup with 2 sequential laminations. You can look at this option in more detail by clicking the “Get Report” button. The top of the Stackup Planner report summarizes your board information, telling you the part number, the revision number, the PCB size, the number of layers, the PCB thickness, the material selection, and your choice for signal or plane outer layers. The green line at the very top and bottom represents the solder mask, with the layers in-between.
In this Stackup representation, you can see:
– The different signals (diagonally shaded representation) and planes (solid orange)
– The dielectric material in-between in green
– The via structures – in this case, this is a through-hole
– The sequential laminations
– The total finished thickness – which comes to 0.069 inches, close enough to the requested thickness of 0.062
– The finished copper weight
The tool also shows different levels of technologies which are corresponding to the feature sizes.
Sierra created the Technology Level categories to give you a better sense of the level of technology sophistication required for different traces and different via sizes. The higher the technology level, the finer the via and trace features. For instance, Technology Level 2 requires finer features than Technology Level 1. As you go up the technology levels, your relative cost is going to be higher. This cost index gives you the relative cost differences you can expect for different technology levels.
The Via Set Information section shows you all the possible vias that can form based on these 2 sequential lam designs. You could have a via from layer 12 to layer 3, or from layer 12 to layer 4, and so on. These vias represent the density and complexity of connections that you can have in the Stackup.
Step 4: The Impedance Calculator
If you want to look further into the report, you can click the “Need Impedance Calculations?” button to enter the impedance calculator tied into the tool. When you click on it, you can calculate impedances for any given layer.
For example, if you click on layer 3, the calculator comes up and tells you what kind of model it is – stripline, single-ended, or stripline differential pair. You can choose using the tabs at the top. For instance, you can enter that you need a 50-ohm impedance, and click the “Calculate Trace” button. The calculator shows that for 50 ohms, you need a trace width of 5 mils.
To save this data, click the “Save” button at the bottom. All the calculations saved are added to the “Customer Saved Impedance Results” in the detailed report.
Now, the report can be printed or emailed to your layout designer. You just finished the first step of creating a fantastic HDI design!