Patterned Die Attach Material for MEMS Stress Isolation

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Solution Overview

Problem

Conventional die attach techniques struggle to form a central adhesive-free zone on microelectronic devices, particularly for stress-isolated MEMS devices with stress relief trenches, due to inaccuracies in material alignment and uncontrolled flow of die attach material during bonding to leadframes.

Innovation Solution

The method involves printing die attach material in a predetermined pattern onto a wafer before singulation, creating controlled voids over stress relief trenches and backside cavities, and partially curing the material to prevent distortion, ensuring the material only contacts the outer peripheral portion of the die during bonding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If die attach material is dispensed over the die flag prior to die placement, then the die can be bonded to the leadframe, but the material may uncontrolledly flow into stress relief trenches and fail to form a central adhesive-free zone

Engineering Contradiction:

Improvealignment precision of die attach materialVSAvoidcomplexity of die attach process

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by printing the die attach material in a predetermined pattern directly onto the wafer before singulation. This advance preparation ensures the material is already positioned correctly on each die, eliminating alignment issues during subsequent die placement. The material is printed to exclude central regions corresponding to stress relief trenches, creating the adhesive-free zone in advance rather than relying on precise alignment during bonding.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If die attach material is applied in a predetermined pattern to exclude central regions, then stress isolation is preserved, but the packaging process becomes more complex

Engineering Contradiction:

Improvestress isolation capability of MEMS deviceVSAvoidcomplexity of material application process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the die attach material application step with the wafer-level processing stage. By printing the material directly onto the wafer before singulation, the process combines material deposition with existing wafer fabrication steps. This integration eliminates the need for separate, complex alignment and application procedures that would be required if the same patterned application were performed at the individual die level.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the spatial parameters of material application by transitioning from individual die-level dispensing to wafer-level printing. This parameter change allows the die attach material to be applied in a predetermined pattern across multiple dies simultaneously, creating the adhesive-free zone through controlled material placement parameters rather than through complex mechanical alignment procedures.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If die attach material is applied at the individual die level, then precise control over material placement is possible, but the packaging productivity is reduced

Engineering Contradiction:

Improvepackaging process throughputVSAvoidprecision of material placement

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent merges multiple individual die processing steps into a single wafer-level operation. By printing the die attach material pattern directly onto the entire wafer before singulation, the process handles multiple dies simultaneously rather than sequentially. This consolidation dramatically increases productivity while maintaining precise material placement through the printing process, which inherently provides controlled material deposition in the predetermined pattern.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively preserves the stress isolation capabilities of MEMS devices by avoiding die attach material infiltration into stress relief trenches, maintaining mechanical decoupling and reducing mechanical stress transmission, while also simplifying the packaging process by applying the material at the wafer level.

Implementation Method 1

The adhesive is partially cured

Methodology Applied

Scientific EffectThermal energy: Heating

Data Source

PatentUS8962389B2Microelectronic packages including patterned die attach material and methods for the fabrication thereof

Publication Date: 2015.02.24 STMICROELECTRONICS INT NV

AI summary

Embodiments of microelectronic packages and methods for fabricating microelectronic packages are provided. In one embodiment, the fabrication method includes printing a patterned die attach material onto the backside of a wafer including an array of non-singulated microelectronic die each having an interior keep-out area, such as a central keep-out area. The die attach material, such as a B-stage epoxy, is printed onto the wafer in a predetermined pattern such that the die attach material does not encroaching into the interior keep-out areas. The wafer is singulated to produce singulated microelectronic die each including a layer of die attach material. The singulated microelectronic die are then placed onto leadframes or other package substrates with the die attach material contacting the package substrates. The layer of die attach material is then fully cured to adhere an outer peripheral portion of the singulated microelectronic die to its package substrate.