PCB HDI
Traditionally, PCBs use through-hole vias for connections between layers. However, with higher component densities in electronic devices, it’s important to route signal lines as efficiently as possible. Microvias help to do just that. This high-density interconnect technology uses blind buried holes that are filled with epoxy resin and copper then capped. These holes connect to the component solder lands in an efficient and cost-effective manner. Moreover, microvias reduce inductance by eliminating signal stubs. This in turn decreases both radio frequency (RF) radiation and electromagnetic interference (EMI).
Microvias are drilled using laser technology. This ensures precision and consistency, reducing the chance for issues that would otherwise negatively affect the performance of the via. It’s also worth noting that the choice of material used to fill the microvias is a crucial factor for both reliability and signal integrity. Copper is an excellent choice as it’s well-suited for conductive filling, and it also has the ability to dissipate heat effectively.
The pcb hdi substrate material must be chosen carefully too, as it impacts both mechanical strength and thermal stability. It should also be compatible with the drilling and metallization processes. Finally, the material should provide the required electrical properties. In particular, it’s important that the copper foil thickness be just right to maximize conductivity without causing problems during etching.
What Sets Microvias Apart From Traditional Vias in PCB HDI?
Stacked microvias resemble through-hole vias and connect in the z-axis between layers. However, stacked microvias have been associated with increased failure rates in recent years. This is thought to be due to a mismatch in CTE between the dielectric and the copper. Dielectrics expand at a lower rate than copper at elevated temperatures, which leads to stress at the metallurgical junction between the microvia and the adjacent copper layer.
On the other hand, staggered microvias have been shown to have more consistent reliability than stacked microvias. They also require less copper, which cuts down on costs. In addition, they enable designers to move the drill position away from overcrowded areas of the board. When it comes to choosing the size of a microvia, a smaller aspect ratio is preferable. This is because larger aspect ratios can result in voiding, which increases failure rates.
However, the precise relationship between void size and failure rate depends on the shape of the void and volume void fraction. It’s also worth noting that copper wrap plating may mitigate these effects. Nevertheless, it’s not uncommon for high-end microvias to fail as the result of voiding. For this reason, it’s important for PCB designers to understand the risks involved and use appropriate metallization parameters to minimize these issues.