Wedge Design Approach – Thinking Document

7/30/2019 Wedge Design Approach Thinking Document

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[email protected], Started 7/17/12

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Wedge Design Approach

Thinking Document
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Causal Analysis and Interactions for Bond Formation

Two Causals for Bond Formation to consider in Wedge Tool Design.

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Components of Wedge Tool

Every wedge tool contains the following components to keep in mind when designing and/or discussing wedge tools



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Bond Cycle Outline Ribbon Front Cut

First Bond

Rapid move to search height

Constant velocity to Touch Down and over-travel position Bond Material touches substrate and forms under tool

Tail may slide on surface if angled downward

Material may slide on heal of wedge if constraints allow

Start Force and Start Power are applied

Wedge coupling increases and energy is transferred to bond interface through bond material

Depending on initial coupling between wedge and bond material:

Wedge may move relative to bond material

Bond material may move relative to substrate

As energy is introduced to system, substrate may start to oscillate if clamping is not adequate

Bond interface is initiated as energy into interface exceeds weld threshold

Bond force and Power are applied

Bond formation goes to completion

Due to the constraints of the system either the wedge must stall or the wedge must break free of the bond at the end of the bond

process. Energy is still being introduced with no change in U/S drive or loading conditions after the bond forms completely.

Tool lifts and proceeds to second bond and repeats the cycle

Hop back and Cut

Depending on cut parameters, ribbon is formed under the wedge tip and the ribbon is cut

Wedge Design and Learning Overview

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What have we learned Al Ribbon

Build-up at the root of the grooves appears to start at the tail and guide edges of the ribbon tools and then grows inward

towards the center

Build-up can be reduced by using higher forces and lower bond powers This can reduce the bond strength

(Not Substantiated with data only hearsay) Build-up appears to be surface roughness dependent

Laser made wedges react differently than production wedges as found in testing of the 127463-4008


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What have we learned Al-Cu Ribbon

Initial penetration is difficult due to hardness of Cu ribbon as compared to Al ribbon

Tool slides down slope of ribbon due to stiffness and position of ribbon guide

If this occurs at touch down, it can cause excessive tail scraping.

Modify the cut and break move to form ribbon under tool more effectively (if possible)

If this is occurring during the over-travel move, the tool could be redesigned to reduce the contact

area at the heal

During the deformation process, the copper flow can cause erosion

Wedge Tip design needs to consider where the material can go during the bond formation and tip

filling process If the material becomes trapped/constrained the pressure on the features can be

destructive

Once the bond formation starts

First bond - constraints exist between the wedge, substrate, and guide.

If the tool does not constrain the tail, vibration in the tail may occur, potentially damaging

both the die and the wedge due to oscillating stresses.

Second bond constraints exist between the wedge, substrate, guide, and ribbon loop.

The constraint between the wedge and loop can vary depending on loop height.

Bond energy can be transmitted/absorbed by the bond, the ribbon at the guide, the loop if present,

and the substrate depending on clamping.

This energy can damage both the first bond heal and the bond interface

Wear on the wedges can be asymmetric depending on the wedge design

It has been seen that the wear is different between the tail and guide sides of the wedge features

Bond testing should be accomplished using bond routines similar to those applied for final designevaluations.

If single bond testing is used, the bond dynamics must be considered when evaluation of the wear

is done.


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New Wedge Design Considerations

Target Material

Target bond area Length and Width

Total Deformation Desired

This is multi phase as there will be the initial Cold penetration and the U/S driven

penetration/deformation

This is also a combination of wedge penetration into the bond material and the

deformation of the material between the wedge and substrate This assumes that the substrate is not subject to any material flow.

Design features to constrain the tail without damaging the heal side ribbon

transition of second or stitch bonds

Design features to reduce side slip of the wedge



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Wedge Design Process

Based on the learning accomplished in this KB (Comparison of Wear Behavior in Copper Ribbon Wedge Designs) a new approach to

tool design is hereby proposed.

1. Select a type and acceptable range of bond material

a) Ribbon/Wire

b) Thickness/Diameter

2. Select a target wedge FL based on target bond length

a) This FL must also be accompanied by Front and Back Radii

3. Create a blank of the desire FL with target Front and Back Radii.

a) For ribbon, this blank will need to have a coupling feature on it of a height equal to 1/5 the target ribbon thickness to enable the

bonds for loop form analysis. (Note: This is only for evaluation of the bending function of the ribbon and not intended to be part of

the tool design.)4. Using the created blank, perform standardized looping and tool form testing.

a) Collect either high speed video (HSV) and pull images just before the bond material touches, at touch, at over-travel, and after

bond formation for each bond condition (IE first, second, stitch).

5. Based on the observations and data collected from the previous evaluations, new wedge design can proceed.

a) Using the images establish the ideal curvatures for both bond 1 and 2.

Note: This will require a compromise for the wedge design as the constraints change on the tail side of the wedge due to bond

and loop conditions.


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