Introduction to microvias technology.

Microvias are small holes in the range of 50 -100 µm. In most cases they are blind vias from the outer layers to the first innerlayer.
The development of very complex Integrated Circuits (ICs) with extremely high input/output counts coupled with the steadily increasing clock rates has forced the electronic manufacturer to develop new packaging and assembly techniques. Components with pitches less then 0.30 mm, chip scale packages, and flip chip technology are underlining this trend and highlight the importance of new printed wiring board technologies able to cope with the requirement of modern electronics.
In addition, more and more electronic devices have to be portable and consequently systems integration, volume and weight considerations are gaining importance.
These portables are usually battery powered resulting in a trend towards lower voltage power supplies, with their implication in PCB (Printed Circuit Board) complexity.
As a result of the above considerations, the future PCB will be characterized by very high interconnection density with finer lines and spaces, smaller holes and decreasing thickness. To gain more landing pads for small footprint components the use of microvias becomes a must.

Introduction to Micro-Chemical-Vias technology.

There are three well know techniques for making blind vias: laser drilling, plasma drilling and photo-imaging. Each o them is very complicated and what is very important there are expensive.
The technique invented in CERN is using chemical reactions to obtain blind microvias.
The advantages of this manufacture with regard to the other technologies are:

·        Reduction of the cost of manufacture.
·        Weak investment needed at the beginning for the realization of the circuits.
·        It is a global process – the time of realization does not depend of the number of produced microvias.  
·        The process is compatible with all the standard assembly lines of printed circuits.
·        Deletion of a stage (perforation) in the manufacture line.

The quality of the final product is better then one obtained from plasma drilling and as good as those made by plasma or photo-imaging. Operating limitations for this technology is 15 µm (e.g. for laser – up to 25 µm).
Using this technique one can perforate vias of any shape (round, star, square, etc.) and dimensions (micron – cm).
The process is compatible with all the standard assembly lines of printed circuits. PCB manufacturer will be able to produce high density circuits, that is for the moment the privilege of companies using laser, plasma or photo-imaging technologies.

Technology process:

Micro-Chemical-Vias are produced in a chemical way. Etching of the Kapton is done in special baths. First the Kapton is processed by standard PCB machinery (for the photolithographic process).  The prepared PCB will be successively located into three chemical baths for specified time.
Special additional conditions (e.g. temperature, fumes restriction) have to be fulfilled. The total processing time depends on the specific layout.

The automotive, computer and telecom industries have embraced microvia technology as a key driver for growth in the high-density interconnection packaging, and reduce layer count designs.

Also rigid-flex application and chip scale packaging alternatives are utilized coated cooper technology. Several large circuit board fabricators currently produce large volumes of board, build with microvia and buried via material enables.

Increased density not only reduces layer count but also enables faster processing speeds.