HDI PCB Manufacturing Methods

HDI PCB manufacturing methods vary depending on the HDI builds, and the common manufacturing is sequential laminating. The simplest 1+N+1 HDI PCB manufacturing is similar to multilayer PCB manufacturing. For example, a four-layer HDI PCB with a 1+2+1 structure is manufactured in this way:

1. The two inner PCB layers are manufactured and laminated, and the two outer layers are manufactured.
2. The two inner layers are drilled by mechanical drilling. The two outer layers are drilled by laser drilling.
3. Blind vias in the inner layers are electroplated. The two outer layers are laminated with the inner layers.
For the 2+N+2 stacked via HDI PCBs, the common manufacturing method is below (take a 2+4+2 HDI PCB as an example):

1. The 4 inner PCB layers are manufactured and laminated. Layer 2 and layer 7 are manufactured.
2. The inner layers are drilled by mechanical drilling. Layer 2 and layer 7 are drilled by laser drilling.
3. Blind vias in the inner layers are electroplated. Layer 2 and layer 7 are laminated with the inner layers.
4. Microvias in layer 2 and layer 7 are electroplated.
5. Layer 1 and layer 8 are manufactured. The HDI PCB manufacturer locates the places for the microvias and drills by laser drilling.
6. Layer 1 and layer 8 are laminated with the finished PCB layers.
Manufacturing 2+N+2 staggered-via HDI PCBs is easier than 2+N+2 stacked-via HDI PCBs because the microvias do not require high precision for locating and stacking.

In HDI PCB manufacturing, besides sequential laminating, technologies for creating stacked vias and in-hole metallization are also in use. For the higher HDI builds, the stacked vias in the outer layers can also be directly drilled by laser. However, direct laser drilling requires extremely high precision for the drilling depth, and the scrap rate is high. So direct laser drilling is seldom applied.