Divisional Silicon Facility - Bond Lab

Recommendations for the design of hybrids

(from the bonder's perspective)

You may obtain support in all phases of the hybrid / PCB fabrication (design, layout, production) by the EST-DEM group.

The bond surface.

The main criteria from the perspective of bonding:-

1.The material and its structure are compatible with the available method of bonding. In the   case of the DSF the method used is Aluminium wedge bonding. 

2..The bond surface should be clean and free from all contaminants. Contamination sources are many and varied, from the obvious such as a fingerprint to the more subtle and less obvious.

3.The bond surface should be flat and of a consistent thickness and quality with no surface damage or irregularities. 

4.The bond surface metal should be of a comparable hardness to the bond wire used. 

5.The bond surface metal is bondable. This can be tested using the bond pull test.

Shape and Size of Bond Pads.

This aspect of bonding is very much dependant upon the method of bonding that is foreseen, Aluminium wedge bonds need a more rectangular bond pad form whereas gold ball bonds favour a more square form pad. It is not to say a wedge bond cannot be bonded on a square pad, but one must keep in mind the pad size with respect to the size and form of the bondfoot in three dimensions. From a Hybrid point of view it is prudent to make the bond pad as large as is realistically possible. This allows a greater flexibility with respect to placement of the bond, placement of the die and fiducial to bond pad repeatable registration. 

 

Pitch and Placement of Bond Pads.

A bond pitch of 60my is possible with 25my wire, but the loop will be limited in height due to the nature of the Double Side Relief Tool which is necessary for fine pitch Aluminum wedge bonding.

 

Double side relief tool

... another view

 The thermal stress effects on the first bond heel by the loop should also be considered when making this choice.  The minimum preferable in line distance between two bonds is 300my, this is tool dependant and to a certain extent loop dependant.

Bondhead Height Tolerances.

Severe complications can result from electronic components (like LEMO connectors) positioned too close to bond pads. Bonding clearance around the tool of the 6400 is shown on this page.

Passivation.

Backside of Hybrid/Pcb.

shape and size of bond pads

pitch and arrangement of bond pads

passivation of PCB / dies

distance to high components

back side of PCB

.....

Status: 24/02/03

(Christian Joram - Ian Mcgill)