Highs Density Interconnects (HDI) printed circuits are now being designed in ever increasing quantities for very high speed applications. The challenge of opto-electronics and integration of photonics down onto the printed circuit
has started to take off. In the next seven years,expectations are that photonic PCBs will grow to a $2.5 billion dollar
industry.
This paper looks at the issues,materials and current processes being researched to create this integrated Opto-
Electronic Circuit Board by European,Japanese and N. American organizations.

There is a growing need in today’s electronic market for high performance Printed Circuit Boards (PCBs) with highspeed signals and enhanced performance. However,they must maintain signal integrity,PCB reliability,quality,and meet the overall thickness constraints of the application. In order to meet these demands,Microvia Technology is utilized to increase design real estate (routing density),improve signal integrity,reduce overall thickness,and enhance PCB reliability. Therefore,Laser Drilling Technology for microvias is fast becoming standard equipment for PCB fabricators in North America. This paper will discuss YAG and YAG/C02 combination laser drilling systems utilized in North America today,compare laser drilling efficiency of microvia materials,and the cost to drill microvias in high performance PCBs.

There is a contingent in the industry that feels reinforced substrates are needed to meet the performance
requirements of HDI microvia technology. Concerns that non-reinforced resin coated foils,or non-woven substrates,
may not provide the thickness control and predictability of movement and reliability needed to meet the next
generation of infrastructure board designs,which must include microvias. Conventional woven glass offerings used
for prepregs which have been fabricated using laser drilling technologies have yielded inferior hole wall quality and
require higher pulse counts making them an undesirable alternative to some.
Development of a laser drillable glass fabric has given new hope to conventional prepregs,offering a better fit to all
attributes desired in materials for HDI microvia applications. Clean hole quality at fewer pulses than conventional
glass fabric,better dimensional performance,dielectric yield control,reduced cracking,ease of handling and storage
and availability make the new generation of laser drillable prepregs an attractive alternative where supported
substrates are desired.
This paper will discuss the attributes and short falls of laser drillable prepregs in comparison to other material types
commonly used in HDI applications.

The combination of high speed and accuracy laser beam deflection,the know-how on wet chemical processes for
Printed Circuit Boards (PCB’s),as well as CAD/CAM implementation for Laser direct Structuring (LS) of PCB’s
together with machine development and construction know-how,resulted in a total laser technology with a
dedicated system (Figure 1),that offers an innovative alternative for the manufacturing of High Density
Interconnection (HDI) technology.
The LS process can easily be integrated into standard PCB production lines,what is proven at a European PCB
manufacturing site. The LS process uses a thin immersion Tin (Sn) as etch resist that is ablated by a focused laser
beam. The laser beam contourizes the circuitry tracks and pads.
The movement of the laser beam is controlled by a high-speed controller,based on electronic CAD-layout data.
This allows to achieve 50 µm space – line structures –and even smaller- without the need for clean room facilities,
with acceptable yields (>70 –80%) and acceptable processing time.
Furthermore,the system has a highly flexible modular construction; a system set-up with a 532 nm (green) or 355
nm wavelength laser proofs to be an excellent structuring as well as µ-via drilling system and this from quality but
also performance view point.

The electronics market demands for smaller,faster,more reliable and less costly products continues to fuel major
changes in printed wiring board designs. Higher layer counts,increasing circuit densities and HDI technologies have
forced the PWB manufacturing industry to find new and unique methods of producing the sub 3mil lines and spaces
required to meet today’s design challenges. Until recently,Laser Direct Imaging (LDI) had been a viable,but cost
prohibitive method of creating ultra-fine line circuitry patterns. Today,new advancements in LDI equipment,laser
technology as well as the introduction of specialized photoresists have allowed LDI to emerge as a production viable
process. Continuing to derail the cost drivers associated with laser direct imaging will further enable LDI processing
to play a leading role in PWB manufacturing today and into the future.

Wireless Communications and Broadband technologies are driving the need for advanced laminate materials with
improved dielectric properties. This paper focuses on new laminate materials with potential uses in multilayer
printed circuit boards (PCBs) for high-speed digital/RF/microwave applications.
The objective of this paper is to discuss the resin structure to property relationship of these new materials. The
primary focus will be on the interaction of various factors,such as,glass,chemical composition and laminate
construction on the dielectric constant and the dielectric loss properties of laminate composites at frequencies in the
2-10 GHz range. This work is focused on epoxy based and non-epoxy based thermoset polymeric resins.

Successful copper plating of blind micro-vias is very strongly dependant on the effective mass transport of copper
ions into the vias. This mass transport limitation is demonstrated by a rough or even in extreme cases at high aspect
ratio or high applied current densities,a burnt appearance of the copper deposit at the base of the via. The poor
quality of deposited copper has an obvious impact on productivity and also on the feasibility of filling the blind
micro -vias required for highest packaging density.
This paper describes the methods used to evaluate solution flow in micro-vias carried out in controlled laboratory
conditions. The subsequent successful implementation of improved solution flow in simulated production equipment
and also in full-scale production is shown. Results are included from horizontal and also vertical processing; in both
cases using production equipment operating with reverse pulse plating and insoluble dimensionally stable anodes.

Laser drilling has clearly captured the technology lead in the formation of HDI microvias with a 78% ownership,1
currently dominating over photo defined,plasma etched and mechanically drilled methods. Processing speeds are
now cutting the costs for laser drilled blind microvias to a level where more and more OEM’s are considering
microvias as an alternative to further fine line technology with its inherent yield issues. This paper will review the
critical elements of microvia processing technology in an overview and focus on the elements that improve yield in
laser drilling. Further,some simple suggestions will be offered to help control and improve yields of laser drilled
blind microvias.

In the Printed Wiring Board (PWB) industry,the growing demand for a higher number of circuit components to be
contained in smaller circuit areas requires that some of the passive components (resistors,capacitors,etc) are now
embedded within the board. This allows for tighter component placement with lower via counts and has also
increased the reliability of these devices.
For thick film resistors,the resistor paste for embedded resistors is screen-printed on the surface of the PWB
laminate (either copper or dielectric) that is patterned according to the circuit design. Current technologies require
wet paste that is oven cured after placement. This paste process results in a resistor with a tolerance of 20-50% from
the target value. Thin film resistors deposited on the PWB also show variation in their values. Resistor trimming is
required to bring this tolerance down to about 1-5% as required by the PWB design. This paper discusses the
implementation of passive resistor trimming for large board manufacturing.

Highs Density Interconnects (HDI) printed circuits are now being designed in ever increasing quantities. HDI brings
some interesting new solutions to age-old signal integrity (SI) concerns,and concerns that will grow as rise-times
continue to drop.
This article focuses on five major areas of SI concerns:
1. Noise
a. Noise-reflections
b. Noise-crosstalk
c. Noise-simultaneous switching
2. Electro-Magnetic Interference (EMI)
3. Interconnect Delays
In each case,HDI offers improvements and alternatives - but it is not a panacea. A couple of 'cautions' are listed that
can be a major stumbling block to HDI implementation,fortunately,they are not SI based. Important to SI is the
materials used in HDI. Although not the focus of this article,the materials selected as well as the dimensional stackup
and PCB design rules will influence SI and electrical performance (impedance,crosstalk and signal
conditioning). Miniaturization provided by HDI will be a major contributor to SI performance. Finally,fine-pitch
BGAs are addressed in term of design rules and layer stackups,all using the improved SI performance
recommendations included in this article