Are Micro Vias Expensive to Produce?
Micro Vias Expensive to Produce
As technology tends towards miniaturization, the need to pack powerful electronics into smaller surface areas impacts not only the electronic products themselves but also the circuit boards that support them. High density interconnect (HDI) design techniques and micro vias enable circuit boards to fit more functionality into small spaces.
Micro vias are a way of replacing through-hole vias in the inner layers of a PCB to improve the routing channels that can be utilized on a printed circuit board. These small structures allow traces to reach the innermost layers of the PCB, allowing a higher layer count and increased signal integrity.
A microvia consists of a blind hole with an internal annular ring with a maximum aspect ratio of 1:1 between the hole diameter and depth. This structure allows a drilled hole to be filled with electro-deposited copper or conductive epoxy and then plated over. There are two kinds of micro vias – stacked and staggered. Staggered microvias are spaced closer together than stacked ones to mitigate issues with thermal expansion and impedance matching between the different copper layers on a PCB.
Are Micro Vias Expensive to Produce?
The size and complexity of microvias makes them more challenging to fabricate than standard through-hole vias. In order to ensure that they meet the industry’s established standards, a manufacturer must make sure that they are positioned correctly and that their internal dimensions are accurate. This is why it is important to submit accurate Gerber files to the fabricator – changes made as an afterthought may affect how well the microvias work.
Achieving the correct tolerances for microvias is complex and requires expert knowledge of both the fabrication process as well as the materials used to create a PCB. The choice of material, as well as its properties such as conductivity, adhesion, thermal expansion, and environmental stability must be carefully considered. This is particularly true for high-performance and industrial applications where reliability is key.
As the use of microvias becomes more common, many questions arise about their cost. Are microvias more expensive to produce than standard through-hole vias? The answer to this depends on the specific requirements of the design, and whether they are stacked or staggered. Stacked microvias increase the number of connections per unit area on a PCB, which can lead to a lower cost per device. However, this also increases the potential for heat generation in the inner layers of the board, and a higher rate of failure due to voiding and copper wrap plating at the butt joint between the microvias.
Staggered microvias help to minimize these effects by distributing the heat load between the individual vias. Staggered vias also reduce the likelihood of a failure due to an electrical short between the bottom of one microvia and the metallurgical junction of another via or copper layer. However, inconsistent results have been reported regarding the effect of voiding on the reliability of stacked vs. staggered microvias, and there is still a lot of research to be done.