In the present as in the past,printed circuit board conductors are sized using simple charts that are a function of
cross-sectional area,current level and conductor temperature rise. These charts do not distinguish between copper
weights,board thickness,and they do not take into account internal copper planes,components,or mounting
configurations. In addition,they do not provide information with respect to the vias,thermals,copper planes or
heavier copper weights.
Research into the current-carrying capacity of electrical conductors has lead to the development of a new IPC
standard to be used for sizing electrical conductors. This new standard is IPC-2152,Standard for Determining
Current Carrying Capacity in Printed Board Design. This new document will deal with conductors in the most
general of terms,that being any metallic media conducting current. This paper discusses where the existing design guidelines
originated and new information that will be incorporated into IPC-2152.

Various Ag-filled epoxies were subjected to a current carrying capability study in which current was applied to the
epoxies at temperatures of up to 170°C for 1008 hours. Test devices with Ag epoxy joint diameters ranging from
7.29 to 9.46 mils were stressed at temperatures of 100°C,150°C,and 170°C. A maximum current of 0.5 amps was
applied,resulting in equivalent current densities ranging from 1003 to 1858 A/cm2,depending on joint diameter.
Data suggests that each high temperature Ag-filled epoxy can survive current densities of up to 1245 A/cm2 when
exposed to temperatures up to 170°C for 1008 hours.
Subsequent cross sections of each epoxy show no indication of electromigration or separation of the Ag particles
after the 1008 hours. The results of this evaluation indicate that high temperature Ag-filled epoxies are capable of
surviving elevated temperatures and high current densities for extended time intervals. This gives a viable lead free
solution for many product assemblies.

Horizontal conveyorized spray processing is the most prevalent method for the production of circuit panels in the
industry today. However,as line and space requirements fall below 4 mils (100µm),the difficulties in producing
panels with high yields and tight tolerances seem to increase exponentially. In the quest for solutions to these
difficulties the seemingly age old question of whether fan or cone nozzles are best for developing and etching high
density interconnects has once again been raised. The fluid dynamics at the surface of the panel are discussed along
with the problems associated with them. The physical properties of the two different types of nozzles are compared
and test data is presented from comparison tests in developing and etching. The conclusion is reached that; while
there are advantages and disadvantages to each type of nozzle,either one is capable of producing good high density
interconnect panels with high yields and tight tolerances in a well-designed spray-processing machine. Going from
one type of nozzle to the other alone is not going to magically resolve problems encountered in producing highdensity
circuit panels.

Predicting printed circuit board (PCB) thickness has not historically been a difficult task. With lower layer count
boards you can afford for the prediction per layer to be wrong by a relatively large amount and still meet thickness
criteria. As layer counts in multilayer boards increase,the ability to predict final thickness after lamination becomes
more difficult and more important. All else equal,as the layer count increases,the error you can tolerate per layer
must be reduced.
This paper discusses a method to design a thickness prediction model for a specific board shop process. This is
accomplished by running carefully constructed experiments and assembling the results into a mathematical
prediction model. The results will show how,in one case,thickness prediction errors were reduced by more than
25%.

Customer demands concerning thermal stability of PCB base materials are increasing. Rising complexity of
printed circuit boards requires an improved quality of the dielectric in terms of cleanliness.
With this background,Multek Europe tested various High-Tg-FR-4 base materials. The tests were divided in
thermomechanical (Cu adhesion,Tg,Time to Delamination,Solder Shock Tests,Pressure Cooker Tests) and
quality investigations (Cu cladding quality,inclusions in the dielectric,HiPot test performance) of the laminate,
characterization of the prepreg (rheological) and a check of the Material Safety Data Sheet.
The paper deals with the tests and their relevance for PCB production or assembly and discusses the results
obtained with the various materials.

In order to evaluate the relative merits of halogenated and alternative flame-retardants used in PWB’s,a comparison
between several different PWB’s each having different flame-retardant packages has been made. The study examines
the leachability of each of the PWB’s,the products obtained from simulated combustion of each PWB,and factory
monitoring of a preferred halogen free PWB. For the combustion tests,incipient fires were simulated using
DIN53436 protocol and tests were carried out at 260ºC and 600ºC in an ISO/TR 9122 apparatus. Leaching studies
were performed using US EPA Method 1311 - TCLP (Toxicity Characteristic Leaching Procedure).

Combination grid-prober (CGP) testing is being
employed with increasing frequency as the density of
SMD lands on boards continues to increase. A
number of factors are at work. Grid testers,as a
stand-alone test methodology,provide a fast and
comprehensive test,but they require costly fixtures
and suffer from intermittent "false opens" when
testing very dense or fine pitch boards. Flying probe
testers,on the other hand,are exceptional in their
ability to handle density and fine pitch,but they
unfortunately suffer from long test times relative to
grids. The test time penalty is so severe,that in some
quick turn environments,fixture test is the preferred
methodology only because lead-time does not exist to
probe the boards. Since the total cost of test is lower
for flying probe than grids below quantities of about
500 boards,some board manufacturers are adding
flying probe capacity in much the same way that
multiple drill machines together provide the capacity
to meet production volume. While this solution may
be satisfactory for some,it is cause to reassess
combination grid and prober testing as a better use of
capital.

Increasing global interest in environmental protection is leading to a higher demand for halogen-free materials that can be
used as the base materials for the printed wiring boards (PWBs) in electronic equipment. These halogen compounds are
under increased legislative scrutiny in Europe as these compounds have been found to form dioxins and furan trace levels
upon incineration. Hitachi Chemical Co.,Ltd. developed halogen-free materials (laminate,prepreg and build-up materials)
for multi-layer boards. Major Japanese OEMs are removing halogen compounds from products and making them
environmentally friendly. The resultant materials satisfy the UL 94V-0 standard without using any halogenated compounds.
Motorola along with Hitachi Chemical developed a strategy to implement the environmentally preferred technologies into
various products based on Market and Competition. In an effort to identify laminate materials,which are acceptable for high
frequency,high performance electrical applications,the characteristics of Bromine,free material was benchmarked with
commercial FR-4 material.
Regarding the flame-retardants other than the halogenated compounds,nitrogen compounds,phosphorus compounds or
inorganic filler are generally known. To achieve UL 94V-0,we need to add a substantial amount of these flame-retardants.
However,these materials influence the properties of PWBs: heat resistance and the pollution rate of medical liquids used in
the production process of the PWBs.
The Japanese resin/laminate supplier has achieved the flammability level (UL 94V-0) by developing an aromatic resinmodified
epoxy,herein termed BE resin. Because this BE resin has an extremely low rate of flammability,due to its aromatic
and nitrogen rich molecule structure,we could reduce the quantity of other flame-retardants.
These halogen-free materials also have good heat resistance,high elastic modulus at high temperature and low coefficient of
thermal expansion. They are able to meet the requirements of PWB manufacturing processes at a higher temperature in
soldering process using a lead-free solder and the highly reliable use of the resin to a thinner and higher-density PWB. Based
on dielectric constant,loss tangent,copper peel strength,glass transition temperature,Z-CTE,ease of processing and plated
through-hole reliability,these materials were assessed in a high performance circuit.

In the best selling book “Who Moved My Cheese”,
author Spencer Johnson tells the story of four
characters—mice named Sniff,Scurry,Hem and
Haw--who are in search of cheese within a maze.
Once they find it,they happily stay put. But one day
the cheese is mysteriously gone. Each character
reveals a different way of handling change when their
cheese has been moved. The story is not unlike the
perils of the circuit board industry. Many changes are
occurring that require circuit manufacturers to find
New Cheese. This paper will reveal how CAM
automation (one flavor of New Cheese) provides the
speed and accuracy needed to survive and compete in
this world of change.

This paper discusses the results of Conductive Anodic Filament (CAF) testing of three types of reinforced microvia
dielectrics using a CAF test specific Printed Circuit Board (PCB). Quantitative results are presented for two CAF
testing modes of failure for microvia layers: HDI layer-to-HDI layer and microvia hole-wall-to-microvia hole-wall.
Some additional data was also collected for the core material conductor-to-hole-wall configuration. The study
demonstrated that a glass-reinforced prepreg and two types of micro-reinforced prepregs,all used in microvia
construction,pass CAF testing. Additional significant factors relating to microvia PCB fabrication and reliability are
presented as they relate to decisions regarding use of CAF resistant materials.
Materials used in PCB fabrication,particularly those containing glass fibers (but not necessarily limited to them),
are susceptible to CAF growth. This growth,if it occurs,will lead to field failures. Often,these field failures are
"self-healing" and the root cause of the failure is not detected. The condition then reoccurs when product is placed
back in service. Other times,the failure is a hard fault and will result in a detectable short circuit. The occurrence of
CAF failures is not just limited to environmental factors; material selection,application,fabrication processes,and
design considerations also impact the growth of,or potential growth of,conductive filaments.
There is much work in the industry to develop and test CAF resistant dielectric materials. As many PCBs are
moving to microvia technology in order to minimize PCB size and maximize PCB function (electrical and design
density),additional factors must be considered when incorporating CAF resistant microvia dielectrics. In particular,
the ability to manufacture high quality and low cost (low material cost and PCB process costs) microvia layers is
equally important to passing CAF. Non-reinforced dielectrics have been shown to be CAF resistant but they can
result in failures from other environmental conditions such as thermal or mechanical stress. Because of these stress
related failures,the industry is moving to the use of reinforced microvia dielectrics as the solution. There are three
classes of reinforced microvia dielectrics: glass fabric,random chopped fiber (e.g. aramid or LCP),and microreinforced
(e.g. expanded PTFE). This paper focuses on two types of dielectric reinforcements: glass fabric and
micro-reinforcement.