Microvias


 

 Introduction to microvias technology.

 

Microvias are small holes in the range of 50 -100 m. 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.

 

 

Conventional
PCB

Microvia
PCB

Size (in²)

18.0

4.5

Number Layers

6

4

Layout Efficiency

25%

80%

Wiring Density (in/in²)

59.7

119.3

Design Rules (in)

.005

.004

Via Pad Size (in)

.027

.014

Via Density (per in²)

100

400

Channel Width (in)

.100

.050

 

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 m (e.g. for laser up to 25 m).
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.

 

 

 

Cell phones require from 250 000 to 650 000 blind microvias per panel. Because of high miniaturization the cell-phone industry takes advantages from microvia technology.  

 

 

 

 

Figure 1.

Global unit mobile phone sales grew 250% in three years and are conservatively estimated to grow to 600 million units in 2005  

 

                                                                                        

Because of high-speed microvias connections, and because of not other possibility PC    computer manufactures have to use this technology.

 Figure 2.         

 Worldwide PC sales have increased  by  15% per year and are expected to  reach 175 million units in 2002


All high-tech portable devices are produced with respect to this machinery.

Figure 3

Worldwide shipments of PDAs are expected to increase by 250% to 18.9 million units in 2003.

Because of total rise in the high-tech mass production, the total value in the microvia techniques rise very rapidly.

Figure 4

Global microvia PCB production has increased by 50% per year and has reached $5.7 billion in 2001.