What is HDI PCB?

HDI PCB is the abbreviation of high density interconnector PCB. HDI PCB manufacturer makes the HDI board by increased layers through micro-blind&buried vias.

HDI PCB board is a compact product specially designed for small capacity users.

The HDI board includes the following via types:

Microvia PCB: In the PCB industry, vias with a diameter of less than 150um (6mil) are called microvias.

Buried vias: The vias are buried in the inner layer, generally not visible in the finished product. 

Blind vias: The blind vias are drills from top layer or bottom layer to a certain inner layer. They are not through the whole HDI board. 

Characteristics of HDI PCB Board

Smaller and Lighter

HDI PCB manufacturer make the HDI PCB board through continuous lamination and laser drilling with a large number of micro-buried blind holes. So it has the advantages of being light, thin, short, and small.

High density

High density interconnect PCB design with more vias, traces, copper pads and inner layers. The via diameter is usually less than 150um, the line width and line spacing do not exceed 76.2um, also the thickness of the interlayer dielectric is less than 80um.

Better Electrical Performance

HDI PCB boards have better electrical performance due to multiple pressing and plating. In addition, the HDI PCB board has better improvement for radio frequency interference, electromagnetic wave interference, electrostatic discharge, heat conduction, etc.

High Requirements For Plug Vias

At present, HDI PCB board buried& blind vias plugging technology is painful for HDI PCB manufacturer. Quality problems will involve vias cavity,uneven dielectric thickness and uneven board edge if HDI PCB manufacturer does not do well with buried and blind vias.

HDI PCB Board Products

Features of HDI PCB Board Manufacturing

The HDI PCB manufacturing process is usually different from that of other standard PCBs, The following are some special characteristics of HDI PCB board manufacturing.

Multiple Laminations

Lamination of PCB core board, PP and copper foil. Unlike other standards PCBs, HDI PCB boards go through the lamination process multiple times. These continuous laminate structures help prevent movement and breakage during drilling.

Via in pad Technology

HDI PCB with via in pad technology is that the via be drilled in copper pad and filled with resin or copper materials. Then plating a layer copper to cover the via, so the pad can be used in soldering.

Filling vias Types

Via filling type should generally be determined based on specific application and PCB requirements. Filling materials used include chemical plating, silver filling, copper filling, conductive resin, and non-conductive resin. The most common via filling material is a non-conductive resin.

Laser Drilling Technology

Laser drilling is widely used in HDI PCB design. The laser heads can produce laser light up to 20 microns in diameter. It’s easy to cut metal and fiberglass and produce very small and clean vias. Using smooth glass fibers with a lower dielectric constant allows for smaller vias.

Fabrication Capabilities

Types of HDI PCB

HDI PCB stackups are classified using the following shorthand: i+N+i where. For example, 2+N+2 stackup would indicate two sequential laminations, and so on for “i” is laminations, “N “ is the number of layers of the inner through layer. Please see below the types of HDI PCB.

Stackup 1+N+1

There is and only one blind& buried drill that directly connects two adjacent layers. For example, layer 1 and layer 2 are connected or layer X is connected to layer (X-1).

Stackup 2+N+2

The blind hole from the outer layer of the via hole to the third layer can be directly connected to the 1-3 layer, or it can be connected to the 1-2 layer and the 2-3 layer separately.

Anylayer

There are micro-vias connections between any adjacent layers. For example, L1-L2,L2-L3,L3-L4,L4-L5,L5-L6,L6-L7,L7-L8… etc.

HDI PCB Manufacturing Process

Inner Layer

The first step is cut material sheet into working panel, then start to make Inner Layer that uses dry film to transfer PCB pattern to the copper clad by exposure and development processes.

King Sun PCB’s inner layer production capability is presently 3mil line/3mil space for Hoz and 1oz copper.

Black Oxide Coating

Black oxide makes core to have a uniform fluff layer that increases the bond strength between the copper foil and prepregs. It also removes grease and burs from the material surface to ensure cleanliness before lamination.

Inner Layer Lamination

This lamination is made for blind vias and buried vias layers. The first step is stack and fix the prepreg sheet and the oxidized inner layer board in position. Then laminated the copper foils, prepregs and inner layer through automatic pressing machine. 

Some HDI PCBs are multiple laminations for different PCB blind&buried vias designs.

Stackup 1+N+1: This HDI PCB type is one time lamination.

Stackup 2+N+2: This HDI PCB type is twice laminations.

Stackup Anylayer: This HDI PCB type is multiple laminations.

Inner Layer Drilling(blind and buried vias)

After first lamination, then blind vias and buried vias will be drilled.

When the via diameter is more than 0.2mm, we will use traditional CNC drilling machine.When the via diameter is less than 0.2mml, we will use laser drilling.

Inner layer Plating

After blind vias and buried vias be drilled, the vias need to be plated before outer layer lamination. Board thickness and via diameter aspect ratio is not more than 10 to ensure the via wall plating is good.

Outer layer Lamination

The next PCB manufacturing processes are as same as standard multilayer PCB.

The Application of HDI PCB

• Mobile communication devices and notebook computers. Moreholes, light weight, small size, strong function.
• Computer and network communication equipment and large equipment. Few holes, high layer acounts, impedance control for transmitted signal trace.
• Chip carriers for LSI packaging, including pads and flip chips, etc.Small line width and spacing (generally less than 2 mils), high precision, small aperture (1-2 mils), small aperture spacing (≤5 mils), good heat resistance, and small thermal expansion coefficient of the substrate.

Why choose us?

Quick Turn PCB Fabrication

We can make PCB prototypes with a very fast turnaround lead time:

Complex PCB Technologies

We make very complex and special PCBs like below:

• Via in Pad PCB
• Embedded Copper Coin PCB
• Backdrill PCB
• Depth Slot PCB
• Countersink Hole PCB
• Blind and buried vias PCB