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HDI PCB – High Density Interconnect

What is a HDI board-pcb hdi definition-hdi pcb manufacturer

What is a HDI board?

HDI stands for High Density Interconnect. The technology used in printed circuit board (PCB) manufacturing allows for a higher concentration of electronic components and interconnections in a smaller area.

The HDI PCB manufacturer makes the HDI board by increasing layers through micro-blind and buried vias. This technology is commonly used in compact electronic devices such as smartphones, tablets, and wearable devices, where space is a premium.

The HDI board includes the following visa 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 a top layer or bottom layer to a certain inner layer. They are not through the whole HDI board.

Characteristics of HDI Printed Circuit Boards

Smaller and Lighter

HDI PCB manufacturers make the HDI PCB board through continuous lamination and laser drilling with many micro-buried blind holes. So, it has light, thin, short, and small advantages.

High density

High-density interconnects PCB design with more vias, traces, copper pads, and inner layers. The diameter of the via is usually under 150um. The line width and line spacing are not more than 76.2um. Additionally, the interlayer dielectric is less than 80um thick.

Better Electrical Performance

HDI PCB boards have better electrical performance due to multiple pressing and plating. The HDI PCB board is also better at reducing interference from radio frequencies and electromagnetic waves. It also helps prevent electrostatic discharge and conducts heat more efficiently.

High Requirements For Plug Vias

Currently, HDI PCB board buried& blind vias plugging technology is painful for HDI PCB manufacturers. If the HDI PCB manufacturer doesn't handle buried and blind vias well, quality issues may arise. These problems include a vias cavity, uneven dielectric thickness, and uneven board edge.

Features of High Density Interconnect PCB Manufacturing

The high-density interconnect PCB manufacturing process usually differs from other standard PCBs. The following are some special characteristics of high-density interconnect PCB manufacturing.

Multiple Laminations

Lamination of PCB core board, PP, and copper foil. Unlike standard 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 uses via in-pad technology. The first step is to drill through holes in the copper pads and fill them with resin or copper material. Then, a layer of 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 the specific applications and PCB requirements. Some of the materials used for filling include chemical plating, silver, copper, 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.

high density interconnect Fabrication Capabilities

Item Technical Parameters Specification
Min Circuit Line Width/Space 2.7/2.7 mil Finished Copper Thickness H oz
Min PCB Pad Ring of Via 3 mil Distance between hole edge to ring outskirt
 Min PCB Pad Ring of PTH 5 mil Distance between hole edge to ring outskirt
 Min PCB Via Size 3 mil Board Thickness < 1.2 mm
 Min PCB Thickness of 4 Layer 0.4 mm Final Board Thickness
Min PCB Thickness of Multilayer 0.4 mm Final Board Thickness
Max PCB Thickness 3.2 mm Final Board Thickness
 Max PCB Dimension 609×450 mm Single and Double Sided  PCB
 Space Between Line to Board Edge 10 mil Milling of Outline
 Max PCB Layers 40 Layer  
PCB Solder Mask Color Green, Black, Blue, Red, White, Yellow  
PCB Silkscreen Color White, Black, Yellow  
PCB Surface Finishing HASL, ENIG, ENEPIG, ImAg, ImTin,OSP, Hard Gold Plating  
Max Finishing Copper Thickness 2 oz  
Dielectric Thickness 2.5 mil  
PCB Material FR-4, Aluminium substrate, Rogers4350C, Polyimide  
Special Technology Countersink hole, Via in Pad PCB,Blind&Buried PCB  

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).

Types Of HDI PCB-high density interconnect-KingsunPCB
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.

Types of HDI PCB-HDI PCB manufacturer-KingsunPCB

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.

Types Of HDI PCB-HDI printed circuit boards-KingsunPCB

HDI PCB Manufacturing Process

Inner Layer

The first step is to cut the material sheet into the working panel, and then make an inner layer. Uses dry film to transfer the 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 gives the core 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 to stack and fix the prepreg sheet and the oxidized inner layer board in position. Then, the copper foils, prepregs, and inner layer were laminated through the automatic pressing machine.

Some HDI PCBs are multiple laminations for different PCB blind and 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 has multiple laminations.

Inner Layer Drilling(blind and buried vias)

After the first lamination, start drilling blind and buried holes.

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

Inner layer Plating

After blind and buried vias are 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 the same as standard multilayer PCBs.

The Application of HDI PCB

  • Mobile communication devices and notebook computers. More holes, lightweight, small size, strong function.
  • Computer and network communication equipment and large equipment. Few holes, high layer accounts, and 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:

Layer Count Standard Lead Time Quick Turn Around
1-2 Layer 4-5 DAY 24 Hours
4 Layer 5-6 DAY 48 Hours
 6 Layer 7-8 DAY 96 Hours
 8 Layer 9-10 DAY 140 Hours
 10 Layer 10-12 DAY 192 Hours

Complex PCB Technologies

We make very complex and special PCBs like below: