High Density Interconnects (HDI) and Micro Vias
High Density Interconnect PCBs contribute to the miniaturization of electronics. GPV supplies 3 types of HDI PCBs, TYPE I, TYPE II and TYPE III, all in compliance with IPC/JPCA-2315. Blind vias can either be laser drilled or mechanically drilled. Buried vias are epoxy plugged and two technologies for the build up can be used.
Background
As the electronic industry continues to push the envelope of extreme miniaturization, product development teams are being forced further into the realm of high density interconnect and micro via technology. Design techniques labeled exotic only a few years ago are now considered mainstream. In particular, build-up substrates usage has grown dramatically, and is now found in a large percentage of high end production electronic products.
Laser drilling and mechanical drilling
For the production of blind vias, GPV today uses the processes of laser drilling, with diameters of down to 0.1 mm, aspect ratio (length of hole divided by hole diameter) is typically 0,8 and mechanical formation with diameters down to 0.2 mm (plated diameter is 0.15 mm), maximum aspect ratio is 8.
HDI PCBs can be supplied with conventional glass-reinforced epoxy and resin coated copper foil (RCC), of which the dielectric has a maximum thickness of 0.05 mm. The choice depends on:
- The product end-use environment
- Expected operating life
- Dielectric withstand voltage
- Resin content to fill buried vias
- Dielectric constant
In other words, the thickness and the type of dielectric are the most important parameters in deciding which material and build-up to use.
Two technologies for the build-up of a HDI
A: SBU (Sequential Built Up) with mechanically drilled through-holes, blind and buried vias, the example is a 6-layer PCB with epoxy filled buried vias.
SBU build-up via formation
B:RCC foil or prepreg and copper foil and Laser drilled blind vias mechanically drilled and plugged buried vias and conventional through-holes, the example shown is a 6-layer PCB. The HDI construction may be IPC/JPCA-2315 Type as well as Type II, refer to diagram below.
RCC foil or prepreg and copper toil build-up via formation
Below are 3 types of HDI constructions described, the text is from IPC/JPCA-2315, Design Guide for High Density Interconnects (HDI) and Microvias. Please consult our front end engineering for best build up's.
IPC/JPCA-2315 Type I HDI Construction
This construction describ-es an HDI in which there are both blind vias and through vias used for interconnecttion. Type 1 constructions describe the fabrication of a single blind via layer on either one or both sides of an PCB sub-strate core.
The PCB substrate is typically manufactured using conventional PCB techniques. The substrate can have as few as one circuit layer or may be as complex as any number of inner layers.
IPC/JPCA-2315 Type II HDI Construction
Type II constructions have the same number of HDI layers as Type I. The core can also be single-sided, double-sided or multilayer as Type I. The main dif-ference is the core con-struction. In a Type II, the buried via holes only connect the outer and inner layers of the core. The example shown is a Type II construction, which has two buried vias in the core sub-strate formed prior to applying the HDI dielectric layers. Both vias connect layer 2 to layer n-1. The buried via on the right is filled with dielectric paste. The buried via on the left is filled with HDI dielectric.
IPC/JPCA-2315 Type III HDI Construction
Type III constructions describe an HDI in which there are plated microvias, pastefilled holes and through vias used for inter-connecttion. Type III constructions are distin-guishhed by having at least two microvia layers on at least one side of a substrate core. The sub-strate core is usually manufactured using con-ventional PCB techniques, may be rigid or flexible, and have as few as one or as many as any number of layers with buried vias.