Background
With High Density Interconnect (HDI) technology, higher packing densities can be realised for electronic components. HDI PCBs offer finer conducting structures and smaller plated through holes. The microvias create space as well as offering improved electrical properties in comparison with traditional plated through holes or blind vias.
Due to the connection of multiple layers, signals can be conducted to the inner layers and be rewired there without blocking the space for components with a high pin density. Depending on the layout, it is even possible to position these components on the PCB with an opposite overlap. Thin PCBs with structures of 100 µm and 125 µm enable controlled impedance conductors for high frequencies.
Parameter | Standard | High standard |
Number of layers | 1-18 | >18 |
HDI lay-ups | Up to 3 x 3 | 4 x 4 |
PCB thickness | 0.6-3.2 mm | 0.6-3.2 mm |
Maximum PCB size | 584*575 mm² | 584*575 mm² |
FR4 materials: Glass transition temperature | 140°C, 150°C, 170°C | >170°C |
Glass fabric | 106, 1080, 2116, 7628 |
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Copper foils | 18 µm, 35 µm, 70 µm, 105 µm | 210 µm, 400 µm |
Inner layer thickness | 75 µm, 100 µm, 150 µm, 200 µm, 360 µm, 510 µm, 710 µm, 1000 µm, 1300 µm, 1500 µm | 50 µm |
Min. track width and conductor spacing of outer layer* | 70 µm / 70 µm | 60 µm / 60 µm |
Min. track width and conductor spacing of inner layer* | 60 µm / 60 µm | 50 µm / 50 µm |
Smallest mechanical drill diameter | 0.2 mm | 0.15 mm |
Aspect ratio | 1:6 | 1:8 |
Min. laser drill diameter | 125 µm | 110 µm |
Landing pad diameter | 330 µm | 250 µm |
Laser via aspect ratio | 1:1.5 | 1:1 |
Dimple | >25 µm | 0 – 25 µm |
Outer layer annular ring | 150 µm | 100 µm |
Inner layer annular ring | 200 µm | 150 µm |
Min. solder mask dam* | 80 µm | 50 µm |
Solder mask color | Green, white, black | Blue, red |
Final finishes | Imm. tin, OSP, imm. NiAu (ENIG), imm. NiPdAu (ENEPIG/ENEPAG), Plated NiAu, HAL, Bond Gold, Hard Gold | Imm. silver |
Legend print color | Yellow, white, black | Blue, red |
*: Values dependent on copper layer thickness
"Blind via" is a general term for a hole starting from the surface of the PCB that does not contact all the way through to the opposite outer layer. A common usage is a laser hole from layer 1 to layer 2, for example. Depending on the diameter, the laser holes are infused or completely filled with copper.
Design rules for laser blind via:
Parameter | Standard | High standard |
Min. laser drill diameter | 125 µm | 110 µm |
Landing pad diameter | 330 µm | 250 µm |
Laser via aspect ratio | 1:1.5 | 1:1 |
Stacked vias are blind vias layered on top of each other. They connect three or more layers electrically, e.g. laser holes from layer 1 to layer 3 but with connection of layer 2.
Parameter | Standard | High standard |
Laser drill diameter: Layer 1-2 | 125 µm | 110 µm |
Laser drill diameter: Layer 2-3 | 200 µm | 125 µm |
Landing pad drill diameter: Layers 1 & 3 | 330 µm | 250 µm |
Landing pad drill diameter: Layer 2 | 425 µm | 375 µm |
Laser via aspect ratio | 1:1.5 | 1:1 |
A skipped via is a connection over at least two lay-up layers that directly connects the outer layer with an inner layer electrically without connecting the intermediate layer. Example: Laser hole from layer 1 to layer 3 without connecting layer 2.
Parameter | Standard | High standard |
Min. laser drill diameter | 200 µm | 125 µm |
Landing pad diameter | 330 µm | 250 µm |
Laser via aspect ratio | 1:1.5 | 1:1 |
A buried via is an inner layer plated through holes that does not connect the outer layers. Buried vias can be filled with resin from the surrounding prepregs. Alternatively, the holes can be plugged and, if required, plated over.
Parameter | Standard | High standard |
Drill diameter | 200 µm - 450 µm | <200 µm and >450 µm |
Outer layer annular ring | 150 µm | 100 µm |
Inner layer annular ring | 200 µm | 150 µm |
Aspect ratio | 1:6 | 1:8 |
