Both Mason Hu and John Gulley make valid points about via in pad 
techniques, but I thought I should throw in Merix's 2 cents on the
matter as well.

Mason is right in his statement that laser vias are not always 
slower and more expensive than other methods.  He is definitely
right in his statement that the use of microvias can make the
part less expensive than conventional (drill vias) boards through
layer reduction.  I would add that microvias often make boards less
expensive through size reduction through the increased density which
is made possible by putting vias in pads.

A critical cost factor in comparing the various microvia methods is
the number of vias in pads.  If the number is low, laser may be the
most economical and fastest method (unless it is not done in-house;
then shipping takes time).  Because processes such as DYCOstrate (TM) 
[plasma defined vias -- the process that John mentioned that Merix is
using] are batch processes, boards with a significant number of 
microvias are less expensive than laser defined via boards.  Merix 
defines it as "buy one via, get the rest free".  Because plasma etchers 
are more common at board fabricators than lasers, the plasma defined via 
process has a greater chance of being performed in-house and is therefore 
often quicker regardless of the number of holes. 

Mason's statement about Japan using SLC (IBM-Japan's process) and laser
is valid, but not surprising considering the plasma defined via process
was developed in Switzerland.  In Europe, the plasma defined via process
is more popular.  This is similar to the trends of immersion gold acceptance
in Europe versus OSP acceptance in Japan.  I would say that comparing 
the pricing of laser via boards to plasma via boards has not been very
thoroughly investigated.  Mason may have been comparing Zycon's pricing to
HP-Germany's pricing and if that is the case  you would have to factor in
duty, shipping, and exchange rates as well as board fabrication cost.  For 
the designs that Merix has seen, the DYCOstrate (TM) process has been the most
economical method of producing microvias.

As a whole, microvia technology has advanced very rapidly over the last
few years and is worth investigating by anyone who is interested in reducing
size, weight, and cost.  Its use should not be limited to the issue of
plugged vias.



Glenn Heath
Merix Corporation
503-359-2652
[log in to unmask] 


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