Hi Harlan,

We have been building blind via BGA boards of this type for several large
OEMs over the last 5 years and have had great success.  The nice thing about
the blind vias is that they do not allow the solder to wick down into the
holes. The adhesion is not as good as the traces but this does not seem to
be a problem with our customers and we have built hundreds of thousands of
these boards.  About 40% of our work is currently blind vias and most have
this design.  

Speaking of blind vias, you may be interested in our new process we call
PhotoLink.  It is a new way to build printed circuit boards without drilling
blind via holes. These holes are photographically developed in a
photoimageable dielectric instead of being drilled.  It allows us to reduce
the cost of blind via boards because we do not need the expensive drilling
machines for small hole drilling or the expensive small drill bits.  In many
cases it also eliminates the need for bonding the board together with
prepreg.  We can develope 5 mil holes in 10 mil pads with 5 mil lines and
spaces. Even though smaller lines are possible, the increased density from
the smaller pads allows us to stay with more economical line widths. If this
sounds interesting, we can send you some information.       

I hope I have been of some help,


Sincerely,


Sid Tryzbiak
VP Engineering
Continental Circuits, Inc.
1150 Belle Ave
Winter Springs, Fl 32708





At 01:52 PM 7/29/96 EST, you wrote:
>     Hello TechNetters!
>     
>     Has anyone had any experience with blind vias in BGA pads?  The 
>     BGA is a 225 I/O, 1.27mm" pitch.  The ball diameter is .0295" and 
>     the pad size being considered is .030".  The via hole size is 
>     .012" maximum.  I have had success with vias in pads that go 
>     through the board but I'm concerned about using a blind via in the 
>     BGA attachment pad due to outgassing or some other unknown 
>     problem.
>     
>     Thanks in advance.
>     
>     Harlan
>     [log in to unmask]
>
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