As time and technology have progressed, so has the development of micro-vias.  Even with standard micro-via usage, devices such as 0.30mm (300 micron) micro BGAs have become almost impossible to “track out” due to the limits of laser drilling technology.  To address this issue we have developed a micro-via tower process (eXMVT®) whereby standard micro-vias are placed directly on top of each other, thus reducing via diameter, increasing routeing density and due to the via being filled with solid copper, aiding signal integrity (reduced removal of copper and interconnects on ground planes) and thermal transfer from the outer layers throughout the construction.  Indeed, while the eXMVT® process is seen as an innovation, it is fast becoming a necessity in today’s demanding niche sectors. 

Related to the development of micro-vias is the increasing adoption of flat pad (eXFPT®) technology.  While the process of via in pad for micro-vias is very well used, it does introduce potential process problems during BGA assembly.  The existing micro-via leaves a small indent or dimple in the surface pad, which can lead to voids or ‘out gassing’ during assembly. The cure for this at design stage is to use the conventional “dog-bone” pad-track-pad, whereby one via contains the surface pad, while the other includes the micro-via hole. This method vastly reduces routing density once more.  If the eXMVT® process is used, the laser ablated hole can be placed in the surface pad position, filled with copper and polished flat. The result is a completely flat pad (eXFPT®), on which the device can be placed without the concerns evident with the standard micro-via – absolutely critical on HDI designs.