# What do Construction and Standard/Alternate mean within the PCB fabrication industry?

In the Constructions column, it indicates AxB.

By the looks of it, B is referring to the woven glass material. See pg 7.

• What is the A in Constructions (AxB) and why would anybody care?
• What does the Standard/Alternate column mean?

Source of chart: Isola Group

What is the A in Constructions (AxB) and why would anybody care ?

B tells you the specific weave of glass being used.

A tells you how many sheets of woven glass are used to build that laminate layer.

What does the Standard/Alternate column mean ?

Notice in your chart that lines 1 and 2 are both for a 0.002 inch thick layer.

The Standard/Alternate column tells you that the 1x106 construction is the standard way to achieve this thickness, and the 1x1067 construction is an available alternate way to do it.

As the other answers have said, you might choose to use the alternate construction if the slightly different dielectric constant and dissipation factor suit your design better.

• To understand correctly - if we look at 106, to achieve a thickness of 0.002, would require 1 sheet. To get a thickness of 0.0035", we would need 2 sheets of 106. Is that correct ? Sep 17, 2019 at 20:31
• @efox29, these are cores, so you can't just lay up multiples together. If you look down the chart, you'll see they give two options for 0.0035: 1x2113 and 1x3313. Sep 17, 2019 at 21:32
• I am trying to understand what you were saying. "A tells you how many sheets of woven glass are used to build that laminate layer.". In the table 9th row, has 2x106 with a thickness of 0.0035. Going off what you said, this has 2 sheets of 106 to provide the 0.0035. Or did I misunderstand ? Sep 17, 2019 at 21:36
• Even if they were pre-pregs, you'd need to know how much squeeze-out you were going to get to calculate the final thickness if you laminate multiple layers together. If you care about this level of detail, you should be using a full service fab vendor, and they will be able to take your request for "this many layers with these thicknesses" and return you a proposed stack up with the exact laminate choices from your preferred vendor (Isola, in this case). Sep 17, 2019 at 21:37
• @efox29, yes you're right. I didn't see that there's a 3rd option for 0.0035". Sep 17, 2019 at 21:37

Looks like it is the number of layers of the fiberglass mat used in the PCB layer:

That's from PDF you linked to.

Some PCB layers are made with a single layer of fiberglass matting, others with 2:

It is important that we understand the effect of the glass used in the construction of the core material we give to an OEM. A 2 ply construction vs. 1 ply will give you a different Dk and Df based on the retained resin %of the core

Source: [Isola Group][3]

Dk is a dielectric constant and Df is the loss tangent, they determine how fast signals propagate through the PCB. The problem is if you manufacture a high speed PCB, then switch manufacturers, you may not get the same results. This is why high speed PCB designers are interested in exactly how the PCB's are constructed, because they want their design to function the same way from a different manufacturer.