adminHDI Printed Circuit Boards
High-density interconnection (HDI) printed circuit boards are found in complex electronic devices that demand excellent performance while conserving space. Several important factors must be considered during the design process, including routing widths, via types and sizes, and stack-up construction methods. The use of stacked vias can help meet these requirements and improve PCB manufacturing costs. Stacked vias consist of buried and blind microvias stacked on top of each other to provide an optimized vertical routing solution.
While there are many benefits of using stacked vias in hdi printed circuit board, there are also some concerns. Some of these concerns center on reliability during thermal cycling. The thin copper plating used in a microvia can become fatigued during the thermal cycle and eventually fail, especially at the plated interface between two stacked vias or at the pad interface of a buried and blind via.
These problems can be minimized by careful consideration of the HDI stack-up and via type selection. Sierra Circuits can help you create a robust, reliable PCB with the right stack-up and via structure to ensure your designs perform well.
Stacked Vias in HDI Printed Circuit Boards
Stacked vias are an essential part of the layer-by-layer construction method that is used to build an HDI PCB. This method allows for more complicated via structures and eliminates the need to drill a series of individual layers. The result is a faster, more efficient manufacturing process.
However, a drawback of this method is that it increases the number of steps required to construct the PCB and, in turn, raises manufacturing costs. This is because the HDI boards must be constructed in multiple layers, drilled, and etched in stages before being laminated and drilled again for each new layer.
Another way to reduce the number of steps in an HDI PCB is by using skip vias. A skipped via is a blind or buried via that doesn’t connect to the outermost layer of the board. Instead, it makes a connection to an inner layer of the board and is hidden from the outside. In a conventional 2+N+2 stack-up, for example, a skipped via can be used to make a transition between layers 1 and 2, avoiding the need to implement a blind-buried stack.
Stacking blind or buried microvias also helps to keep the traces on the board smaller, allowing them to fit inside pads for fine pitch ball grid arrays (BGAs). In some cases, this is necessary because normal vias are too large to accommodate these components.
Stacked vias can also help to maintain impedance in the trace, which is vital for signal integrity and proper operation of the circuit. High impedance along the traces can lead to signal distortion and reflection. Keeping the traces as small as possible helps minimize this issue and prevent other electrical problems such as data loss. Stacked vias can also be used to place components close to the ground planes, which improves shielding and reduces electromagnetic interference (EMI). Sierra Circuits has extensive experience designing and producing PCBs with staggered and stacked vias. We take great care to obey the DFM rules for this type of via and will work with you to find the best solution for your specific application.
