The trends of increased functionality and reduced size of portable wireless products,such as handsets; PDAs are demanding
increased routing densities for printed circuit boards. The handheld wireless product market place demands products that are
small,thin,low-cost and lightweight and improved user interfaces. In addition,the convergence of handheld wireless phones
with palmtop computers and Internet appliances is accelerating the need for functional circuits designed with smallest,lowcost
technology.
Historically,the industry has met this challenge through high density interconnect technology and increased silicon
integration and component miniaturization. Microvia high density interconnect (HDI) also known as build up technology,is
one method for constructing circuit boards with high routing density demands.1
For HDI board,vias can be formed using unreinforced dielectric such as Resin Coated Foil (RCF),using processing
techniques such as laser drilling or photoimaging. The vias are then metallized using electroless copper/electrolytic plating.
The advantage of the HDI construction is the ability to create smaller vias (6 mils) and via pad sizes. This enables higher
routing density,lower metal count,reduced board area and increased functionality as compared to conventional boards. HDI
improves the wiring density by using build up microvias in the outer layers. However there is still dead space where
components cannot be mounted and lines cannot be wired,because of staggered via hole structure.
On the other hand,ALIVH-G (Any Layer Interstitial via Hole) needs no through hole. This is because any two layers are
electrically connected by IVH (Interstitial via Hole). The IVH can be placed in any position. Since there is no through hole
that disturbs interconnections between components,the dead space becomes reduced and the wiring capability is improved
greatly.2
Past board technologies used stacked microvias on the outer layers. Current board designs use ALIVH-G technology. These
vias are laser drilled and the interconnection technology used is conductive copper paste. The typical design rule is
Lines/Space 100/100 micron and Via /Land is 200/400 microns. ALIVH-G technology makes a lightweight substrate (less
than 100g)
The paper presents the evaluation conducted to ensure the stability of the laminate and microvias through the double sided
reflow process. This was evaluated as a part of the phone product qualification build.