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Pad Under Via Substrate Method Disclosure Number: IPCOM000005049D
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2001-Aug-01
Document File: 3 page(s) / 34K

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Christopher T. Clark: AUTHOR [+1]


Pad Under Via Substrate Method

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 100% of the total text.

Pad Under Via Substrate Method

Christopher T. Clark

Burton J. Carpenter

Problem: Eutectic bump joints in flip chip packages degrade during reliability stress testing. A

ratcheting effect that results in the bump and substrate ends of the joint to move in opposing

directions relative to each other is one of the most significant contributors to the degradation of

the joint.

Solution: Replace the non restricted butt joint common to eutectic bump joints in Flip Chip

packaging with a mechanically restricted joint that utilizes more surface area of the bump for

connecting die to substrate. The greater surface area contact of the bump will absorb stresses

induced during "ratcheting" as well as provide a mechanical restraint against separation.

Description: This new joint will resemble a pad under a via.

Metal 1: Via Layer Interconnect only

Metal 2: Pad Layer and first distribution.

Eutectic bump with electroplated solder.

One option for the manufacturing process of this type substrate could be to use a lamination

architecture. In this type of substrate, individual layers are made and then laminated together in a

hot press process. The top layer or interconnect layer would have blind vias drilled into the

dielectric of foil. These blind holes could then be plated full with copper and then later

counterbored or 'drilled' with a laser. This type of manufacturing process will also permit a via

without lan. An additional advantage of a via without lan is finer pitch capability. The

interconnect layer using blind vias without lans would be able to permit finer bump pitch

capability with increased surface area contact between die bump and substrate pad and reduce the

effects of ratcheting with this substrate methodology.

It may be that there is no known problem involved and the subject matter is merely a supposed advantageous way of doing a particular thing. In that case, the presentation would be merely "what" and "how to". Similar to a patent specification, reference numerals are used and referred to on an "item by item" basis, although on a somewhat less detailed scale.