A PCB is normally a multilayered board with the simplest being a single layer. Stack-up is the description on arrangement this multi-layered structure. This description is essential to PCB manufacturer in order to make the PCB. One often needs to find the capability of PCB manufacturer first before defining the stack-up. Collaborating with the vendor on the stack-up early in the design will ensure a smoother handoff at the end.
PCB is made by laminating each PCB piece from center to outer layers.
- Each inner piece contains two copper layers sand-witching a core layer
- After copper etching, (removing unwanted copper to form trace and vias) each inner piece is laminated together by adhesive materials called prepreg.
- Via drilling comes after laminating.
- At the outer layers, there will be additional finishing copper plating for the vias adding to the thickness of outer layers.
- Note: There other types of PCBs such as flexes and rigid flexes, please see PCB Manufacturing for more details on Stackup.
Via: it's the hole that connects PCB layers together
Trace: it's the copper wiring that connects IC pins, connector, and electronic circuits, together.
Substrate layer often labeled as core
Adhesive layer often labeled as prepreg, which is made of fiberglass material (substrate) mixed with half cured resin material for "gluing"
Conductive layer often labeled as copper
Stack up is summarized in a table as
- Number of layers
- Description of each layer
- Materials of each layer
- Thickness of each Layer
- Via arrangement for each layer
PCB Technology: High Density Interconnector (HDI) PCB
- Thin and light weight
- Smaller trace width and spacing
- Stacked laser drilled uVias
- Via in Pads for easier signal wiring fanout from finer pitch and dense pin areas under a IC package.
10 Layered PCB Layer Definition
- L1 - Mixed Component and Signal
- L2 - GND
- L3 -Signal 1/2 Oz copper
- L4 - GND
- L5 - Power 1/2 Oz copper
- L6 - Power 1/2 Oz copper
- L7 - GND
- L8 - Signal 1/2 Oz copper
- L9 - GND 1/2 Oz copper
- L10- Mixed Component and Signal
- Total thickness
- any layered vias
- stacked and/or staggered microvias.
SUMMARY & CONCLUSION
- Stackup is the description of PCB layer counts, material used, vias arrangement, and thickness of each layer.
- HDI is the modern PCB technology that allows high density component design
- Prepreg is the glue layer
- copper is the conducting layer
- core is the substrate layer often made of fiberglass.
Due to increasing miniaturization of IC chips and form factors, its common to see HDI multi-layer board with 8,10,12 layers as found in laptops and mobile phones.
Reference and Further reading:
"Tips for PCB Stack Design", https://www.tempoautomation.com/blog/top-4-tips-for-pcb-stackup-design/
"PCB Stackup", http://www.stormcircuit.com/pcb-stackup.html