High-density interconnect (HDI) PCBs are characterized by finer lines, closer spaces, and more dense wiring, which allow for a faster connection while reducing the size and bulk of a project. These boards also feature blind and buried vias, laser ablated microvias, sequential lamination, and via in-pads. As a result, a HDI board can house the functionality of the previous boards used. MADPCB is an HDI PCB manufacturer and provider in Shenzhen, China supports HDI PCB prototype and mass production with less expensive price and quick-turn lead time. Customers from a variety of industries we serve have a common that have high expectations in quality, reliability and on-time delivery in HDI PCB production. Our quality is not afterthought, but built into each process from front-end to fabrication and shipping.

1. High Density Interconnect (HDI) Printed Circuit Board (PCB)
PCB technology has been evolving with changing technology that calls for smaller and faster products. High-density
interconnect (HDI) PCB technology, including laser drill micro-vias, VIP (Via-in-Pad), blind and/or buried vias and build-up
laminations, is one of the most significant advances in PCB manufacturing. HDI printed circuit boards (PCBs) are with a higher
wiring density per unit area than traditional PCBs. Products with HDI PCBs are more compact and have smaller vias, pads,
and traces and spaces. As a result, HDI board can house the functionality of the previous boards used. MADPCB is an HDI
PCB manufacturer and provider in Shenzhen, supports HDI PCB prototype and mass production with less expensive price
and quick-turn lead time. Customers from a variety of industries we serve have a common that have high expectations in
quality, reliability and on-time delivery in HDI PCB production. Our quality is not afterthought, but built into each process
from front-end to fabrication and shipping.
HDI PCB Manufacturing Process
The overall process for manufacturing HDI PCB is essentially the same as for fabricating other PCB board, with notable
differences for PCB stack-up and hole drilling. Since HDI boards generally require smaller drill holes for vias, laser drilling is
usually required. Although laser drills can produce smaller and more precise holes, they are limited by depth. Therefore, a
limited number of layers can be drilled through at a time. For HDI boards, which are invariably multilayer and may contain
buried and blind vias, multiple drilling processes may be required. This necessitates successive layer boding to achieve the
desired stack-up or sequential lamination cycles. Not surprisingly, this can significantly increase PCB manufacturing time and
cost.
HDI PCB fabrication is an advanced technology and therefore requires expertise along with specialized equipment like laser
drills, laser direct imaging (LDI) capacity, and special clean room environments. In order to efficiently manufacture high-
quality and reliable HDI PCB products, you must understand the HDI board manufacturing process and coordinate with your
HDI PCB supplier and provider to implement good DFM (Design for Manufacturability) for HDI layout.
HDI PCB Design
The electronics industry is largely consumer-driven and the directive for smaller more capable products with increased
functionality will only intensify in the years to come. At MADPCB, we are well-positioned to assist you in meeting this demand
with advanced equipment, processes and expertise to manufacture your HDI PCB boards quickly and precisely. Click to learn
more Design for HDI PCBs.
HDI Board Stack-up
⚫ 1+N+1 with laser microvia and mechanical buried core via. The “1” represents “build-up” or sequential lamination on
each side of the core.
⚫ i+N+i (i>=2) – PCBs contain 2 or more “build-up” of high-density interconnect layers. Microvias on different layers can
be staggered or stacked. Copper filled stacked microvia structures are commonly seen in challenging designs.
⚫ Any Layer HDI (ELIC) – All the layers of a PCB are high-density interconnection layers which allows the conductors on
any layer of the PCB to be interconnected freely with copper filled stacked microvia structures (“any layer via”). This
provides a reliable interconnect solution for highly complex large pin-count devices, such as CPU and GPU chips utilized
on handheld and mobile devices.
Laser Drilling Technology
Unlike mechanical drills, the laser drilling process doesn’t physically contact the PCB material that it is working with. Drilling
the smallest of microvias allows for more technology on the PCB surface. The high influence beam of the laser machine can

2. drill through metal and glass to create the tiny via hole. HDI PCBs always have a large laser drilling quantity per square meter,
even more than 50K density since its high-density interconnection, and the laser machine drilling capacity always reaches
4.3million pieces daily.
Laser Drilling Imaging (LDI)
Imaging finer traces than ever before to process these HDI parts is costly but necessary. Finer traces, spacing and annular
ring requires much tighter controls. With use of finer traces, touch up rework or repair becomes an impossible task. Photo
tool quality, laminate prepreg and imaging parameters are necessary for successful process. LDI (laser direct imaging) is a far
better option for such fine traces and spacings.
Via-in-Pad
When micrvias are placed in pads intended to be soldered (Via-in-Pad), the holes should be filled. Vias can be filled and
plated over or filled with copper to yield an acceptable solderable surface. If the vias are not filled, the volume of the microvia
will “steal” solder from the intended solder joint. The air, which is entrapped after solder paste has been applied, is also
likely to out gas during the reflow assembly process and create voids in the solder joints.
In PCB design, via refers to a pad with a plated hole that connects copper tracks from one layer of the board to other layer(s).
High-density multi-layer PCBs may have blind vias, which are visible only on one surface, or buried vias, which are visible o
neither, normally referred to as micro vias. The advent and extensive use of finer pitch devices or products and requirements
for smaller size PCBs creates new challenges. An exciting solution to these challenges uses a recent, but common PCB
manufacturing technology with self-descriptive name, “VIA IN PAD”.
Via in pad helps to reduce inductance, increase density and employ finer pitch array packages. The via in pad approach places
a via directly under the device’s contact pads. This allows higher component density and improved routing. Consequently,
via in pad provides the designer significant PCB space savings. For example, traditional fan-out places four components,
whereas with via in pad, eight components can be placed within the same board outline.
Filled via in pad is a way to achieve intermediate density with an intermediate cost compared to using blind or buried vias.
Some of the key advantages associated with using the via in pad technology are:
⚫ Fan out fine pitch (less than 3mil) BGAs
⚫ Meets closely packed placement requirements
⚫ Better thermal management
⚫ Overcomes high speed design issues and constraints i.e. low inductance
⚫ No via plugging is required at component locations
⚫ Provides a flat, coplanar surface for component attachment
However, there are some disadvantages associated with this technology. The most prominent and worrisome is the cost
impact associated with adopting a new technology. PCB manufacturers and suppliers identified two primary cost drivers
associated with specifying via in pad technology: Additional HDI PCB manufacturing process complexity and the underlying
material cost for the conductive fill.
Specifically, via in pad technology adds 8 to 10 steps to the PCB manufacturing process while via filling cost is a function of
the via size and actual number of via instances on any given design. However, the reduction in layer count realized by using
via in pad technology compensates for the added cost associated with this process.
HDI PCB Materials Selection
Material type and construction is extremely important in designing and manufacturing HDI PCB boards. Designing HDI
interconnects involves an understanding of the potential problems arising when specifying glass reinforced dielectric
materials.
Microvia dielectric materials can introduce misregistration and rough vias whether plasma, laser, or mechanical drilling is

3. performed. Not only are the material properties of the microvia dielectric materials called into question, but also the
consistency of the weave, as well as the quality of the fibers used. The potential to close the weave openings by spreading
the fibers out is extremely important, as this minimizes open spaces that cause skew and drift.
Copper Clad Laminate (CCL)
Copper clad laminate materials have copper foil laminated onto one or both sides of cured (C-stage) dielectric. The typical
application uses single-side clad laminate material where the copper clad is used as the outer layer and the c-stage is bonded
to the sub-composite. Microvia are formed utilizing plasma or laser methods. Materials available differ by reinforcement
(woven glass, non-woven glass and expanded PTFE) and chemistries involved (epoxies, polyimide, polyester etc.).
Resin Coated Copper (RCC)
Resin coated copper materials are compromised of copper foil, coated with a resin dielectric material that can be directly
bonded to the sub-composite. They differ by whether they are wet processable or not. In non-wet processable-coated
copper materials, microvias are formed utilizing plasma or laser drilling methods.
Embedded Electronics Components
Passive components, such as resistors, capacitors and inductors, as well as active components, are referred to as embedded
components when placed withing the substrate of the thru-hole and HDI printed circuit board. These are known as
Embedded Resistor PCB, Embedded Capacitor PCB, Embedded Inductor PCB or Embedded XX PCB. A wide variety of
materials and methods can be used when embedding these circuit functions within the PCB board, and there are a number
of reasons why designers would want to embed components within an HDI printed board. The primary reason is related to
circuit function. In digital circuits clock rate drive the signal rise time. In analog circuits bandwidth drives signal rise times.
As signal rise times decrease and corresponding frequencies increase, the lead inductance associated with discrete, surface
mount components begins to degrade circuit function. Moving the component from the surface of the HDI PCB into the
substrate reduces the lead inductance and parasitic capacitance. Secondary considerations for embedding components are
related to PCB surface real estate and subsequent cost. As frequencies go up and circuits become more complex, more
passives are needed to maintain signal integrity. Increased PCB size adds cost while consumer pressure demands smaller
and less costly products. Embedded components in the printed board frees surface real estate for more functionality and
enables PCB board size reduction with corresponding cost reduction. Finally, a third level of impetus to embed components
is reduction of the overall number of solder joint connections, which could improve overall reliability of the PCB board.
⚫ Embedded Resistor PCB: Embedded resistors are formed within the substrate of the printed circuit board by any of
several methods. The resistive elements are typically formed between two conductors on the same layer. Resistor
chemistries include Nickel/Phosphorus, Lanthanum Boride, Mixed Metal in Organic Matrix, Conductive Polymer, Doped
Platinum, Organometallic, Nickel/Chromium, and Nickel/Chromium/Aluminum Silicon. Some embedded resistors have
an encapsulant applied above, below or both. The encapsulant materials are typically epoxy based.
⚫ Embedded Capacitor PCB: Embedded capacitors are formed within the substrate of the printed circuit board by any of
several methods. There are two distinct differences among embedded capacitor materials. One type is in the form of
an inner layer laminate comprised of a dielectric core having copper or other form of conductor on both sides of the
core. The copper or other form of conductor on each side of the dielectric forms the two plates of the capacitor. The
other type is dielectric applied in discrete locations on a layer with the copper or other conductor initially existing on
that layer forming one plate of the capacitor and a copper or silver-based paste applied as the second electrode. Some
embedded capacitors have an encapsulant applied.
⚫ Embedded Inductor PCB: Embedded inductors are typically made by imaging the copper on one or more layers within
the printed circuit board in spiral patterns, Inductors are also made by applying a ferromagnetic material above, below
or between the spiral conductor patterns.