PCB Fine Lines & Spaces
High density interconnect (HDI) technology, including fine lines and spaces (2 mil and below) is a key enabling technology for the next generation of portable electronic devices. This technology offers many advantages over conventional technologies including PCB size reduction, increased routing, and lower fabrication costs.
Today's trend in portable electronics is to manufacture smaller and lighter products with increased functionality. The size of the products we all use each day are only a fraction of the size they were a few years ago. Increased product functionality coupled with drastic size reduction places extreme demands on designers to increase silicon integration, reduce silicon packaging size, and reduce the printed circuit board size.
Advances in integrated circuit packaging technology such as direct chip attach, ball grid arrays, and chip scale packages have outpaced the ability of the printed circuit board industry to manufacture cost effective mother boards on which to solder the packages.
Printed Circuit Board with Fine Lines and Spaces
Printed circuit board manufacturers must invest in specific equipment and technologies in order to be able to consistently produce circuit boards with 2 mil lines and spaces.
Laser Direct Imaging
A laser is used to image a pattern directly on to a photoresist-coated panel, completely eliminating the production and use of a traditional phototool. LDI (Laser Direct Imaging) instrument measures the precise positions of features or fiducial marks on the panel and then uses these to calculate exactly how the pattern should be altered in order to optimize registration for that unit or batch. This ability to achieve tight registration tolerances can have a particularly significant yield impact on production of PCBs with small design rule tolerances.
Cupric Chloride Etching
Most PCB companies use the pattern plate / strip / etch / tin strip process so ammoniacal etchant must be used due to the fact that cupric chloride will remove the tin or tin / nickel pattern plate applied as a resist along with all of the copper. However, cupric chloride etching is a much more controllable process and with very little effort and the most basic equipment, line and space sizes down to 2 mil can easily be achieved using cupric chloride. Because of the significant cost of purchasing and maintaining 2 etching systems most circuit board manufacturers only use ammoniacal etch for both fine lines and standard technology products.
With the need for fine lines and spaces comes the need for ultra-precise registration in the drilling process. With laser drilling and the automatic registration of the drilling pattern to optical targets (drilled or etched) is this drilling technology's main advantage. With the individual registration and the adaptation of the drilling pattern to the dimension of each circuit board, pad sizes could be reduced dramatically. Microvia target lands have a diameter between 300 µm and 250 µm and they will continue to drop.
Without investing in the proper technologies it is difficult for a PCB manufacturer to manufacturer fine line and space printed circuit boards down to 2 mils.