Any layer HDI PCB
Any-Layer HDI, sometimes also called an ELIC – Every Layer Interconnect HDI, is a PCB where each layer is a microvia-based HDI layer, and all the connections between the layers are made using copper filled microvias. This approach has eliminated the need for PTHs for the surface to the bottom layer connection, since both the outer layers can be connected using stacked or staggered copper-filled microvias. This allows for a higher component density by utilizing most of both surfaces.
Any-Layer HDI is still being developed and refined. Fabricators are experimenting with new techniques and materials, like using specialized pastes for interconnects between the layers. But the technology itself isn’t very original. It’s almost two decades old. Panasonic introduced its first ALIVH (Any Layer Interstitial Via Hole) to the market in 1996. Any-Layer HDI PCBs have found a special place in smartphones, GPU, and CPU circuits, and it’s easy to see why. If you use Any-Layer HDI method to design and fabricate your PCB, instead of the conventional HDI techniques, you will use about 40% of the PCB volume; this saves precious space for other gadgets in the smartphones, making them lighter overall. Any-Layer PCBs first mainstream use is usually associated with Apple’s iPhone 4 and iPad 2. Apart from decreasing the volume of the PCB board, the difference in thickness between an ordinary HDI and Any-Layer HDI is also very significant. The iPad 2 was almost 35% (4.6 mm) thinner than the original iPad because iPad 2 employed a 3+4+3 Any-Layer HDI stack up. A relatively latest example is the Samsung Galaxy S8 that uses a 12-layer Any-Layer HDI stack up. |
The most complex PCB we made is 14 layer with any layer HDI.
Our any layer HDI partner is Foxconn, the top PCB manufacturer in the world. |
Design and Fabrication
Any-Layer PCBs can be designed as a core-based PCB, or they can be core-less (IPC Type VI Stackup). Since the Any-Layer HDI doesn’t have any PTH, there isn’t any drilling required after lamination. When you are building with Any-Layer HDI, each HDI layer that is to be stacked on the core’s either side acts as a separate circuit. In each PCB layer, microvias are drilled, then they are filled and plated over, then they are printed over and etched, and finally laminated. If other layers are to be stacked on top, they go through the same process: Drilling, filling, plating, printing, etching, and lamination. If they are working with a plated core, the PCB might have to go through five trips for a 4+2+4 stack up.
But sequential lamination build-up with multiple cycles isn’t the only way. In some cases, a Z-axis conductor paste is applied between all the filled microvias that need to be connected, prior to lamination. And then the layers are laminated together. This reduces the number of lamination cycles required.
Some top-of-the-line fabricators use the Any-Layer Interstitial Via Hole (ALIVH) for Any-Layer HDI fabrication. In it, usually, the microvias are drilled in the prepreg, they are filled with either copper paste or another conductor, which hardens when that HDI layer is laminated. When the layers are ready to be lined up, a unique metallization technique is used to interconnect via holes. This method is a lot superior, both in terms of connectivity, and thermal dissipation, to simply stacking up filled microvias.
Better interconnection of microvias and heat management allows for a higher layer count with Any-Layer HDIs than what might be possible with conventional means.
But sequential lamination build-up with multiple cycles isn’t the only way. In some cases, a Z-axis conductor paste is applied between all the filled microvias that need to be connected, prior to lamination. And then the layers are laminated together. This reduces the number of lamination cycles required.
Some top-of-the-line fabricators use the Any-Layer Interstitial Via Hole (ALIVH) for Any-Layer HDI fabrication. In it, usually, the microvias are drilled in the prepreg, they are filled with either copper paste or another conductor, which hardens when that HDI layer is laminated. When the layers are ready to be lined up, a unique metallization technique is used to interconnect via holes. This method is a lot superior, both in terms of connectivity, and thermal dissipation, to simply stacking up filled microvias.
Better interconnection of microvias and heat management allows for a higher layer count with Any-Layer HDIs than what might be possible with conventional means.