Standard and predefined build-ups
A few months ago, prepreg construction 2125 was removed from the available prepreg list of 370HR and IS400, 2 of our main FR4 material types. We exchanged this prepreg type with construction 2116. The thickness of 2116 differs from the 2125 with approximately 20 µm. At first we assumed it wouldn’t have much influence on the final thickness of the boards.
Only, some of our standard build-ups contained many sheets of this type – our standard 6-layer board contained 7 of these – which resulted in an unexpected final thickness, often too thick.
So, we had some work to do: checking out and updating all the build-ups our customers can chose from using the build-up selector.
We take the opportunity now to explain a bit more on how to read and understand the values we show in our PCB Configurator tool, referring to this subject.
The thickness label
This is the value we show in the selection box: Board thickness
This is not the final thickness of the board but a part of the name of a certain build-up. We try to keep the thickness of the actual build-up situated in a range of +/- 10 percent of the label value.
If not, probably due to selection of high Cu thickness, it will be shown.
The Total material thickness
Here we show the sum of all theoretical thicknesses of the used base material:
- Core thickness
- Prepreg thickness
- Cu foil (inner and outer)
NO galvanic Cu deposit (plated Cu thickness) is included.
The final board thickness
The calculated final board thickness is the total material thickness + the thickness of the galvanic Cu deposit on the outer layers and the thickness of all additional layers, such as soldermask, legend… This calculated value should be within 10 percent from the measured value.
How to measure?
Measure on a spot without Cu, add the thickness of the Cu-foil used for the outer-layers plus the galvanic Cu deposit plus any additional layers.
It is important to note that the final thickness of the PCB will vary depending upon many factors, these include the actual base material tolerance (as defined by the manufacture), the plating tolerance, the actual design layout, pooling and its position on the production panel.
There will be variations in Cu thickness across the PCB itself and also between individual PCB’s on the production panel (ref. Plating Index). Our objective is to have a minimum of 20µm Cu deposited (plated) in the holes, the average deposit on the traces is between 25-35µm but there may be peaks of 50µm or more.
The Soldermask thickness may also vary, our objective is a minimum thickness of 7µm, however, the maximum may be much thicker due to the thickness of Cu foil used for the outer layers, the actual thickness of the Cu deposit or if rework is necessary.
Details of the build-up construction
we show in the PCB Configurator tool can be discovered using the mouse-over function integrated in the buildup image.
You can see the core thicknesses, Cu thicknesses and the used prepregs appearing.
In Standard Pool, all our standard and predefined build-ups are constructed using these cores and prepreg types: check our download page with the list of used material types and their datasheets.
- Core: 100, 200, 360, 710 µm (with Cu foil: 12/12,18/18, 35/35 or 70/70 µm)
- Prepreg: PR1080 (70 µm), PR2116 (120 µm) and PR7628 (180 µm)
- Other available core thicknesses: 510 µm, 1000 µm and 1200µm (stock not guaranteed and only used in “special Build-up”; add the build-up construction in your dataset in this case)
In RF Pool, we have 3 additional material types available. (Be aware that not all thicknesses have guaranteed stock)
- RO4350B: 100, 168, 254, 338, 508, 762, 1524 µm (18/18)
- Bold ones are used in standard RF buildups and are also available in 35/35 and have guaranteed stock
- RO4003C: 203, 305, 406, 501, 813 and 1524 µm (18/18)
- Prepreg RO4450F: 100 µm
- I-Tera: 254, 360 and 508 µm (18/18)
- Bold ones are used in standard RF buildups and have guaranteed stock
In IMS Pool, we selected Polyterm TC-Lam 2.0.: 1500/100/35 (Aluminum alloy/dielectric/Cu thickness)