The semiconductor and electronics manufacturing markets are continuing to expand.
A recent report by Fortune Business Insights predicted that the semiconductor market will grow to be worth over US$2,062.59 billion by 2032.
As demand continues to increase, the importance of testing wire bonds grows in parallel.
Wire bonding is widely used in electronic devices, the semiconductor industry, and microelectronics.
It enables interconnections between the die and other electronic components in an integrated circuit (IC), such as transistors and resistors.
Any defects in these bonds can lead to issues like open or short circuits, significantly impacting device functionality.
Therefore, testing wire bonds is not just about ensuring reliability and reducing production costs but also about guaranteeing compliance with industry standards.
Above are some of the common defects that impact wire bonds.
Overview of testing methods
The most widely adopted methods for testing wire bond defects are optical/X-ray inspection using automated X-ray inspection (AXI) and electrical test methods using automated test equipment (ATE).
AXI uses X-rays to penetrate and capture detailed images of wire bonds, detecting hidden defects such as foreign material, voids, and sealing issues.
It is non-destructive and excellent for inspecting complex assemblies.
However, it can be slow and costly, and there are concerns regarding radiation safety.
On the other hand, ATE tests the electrical characteristics of wire bonds, identifying concerns such as open circuits, short circuits, and degraded performance.
It is fast, consistent, and programmable, ideal for high-volume production, but may not detect structural and mechanical defects.
Apart from the electrical and optical test methods, other techniques can be deployed to evaluate the wire bond.
For example, a wire and bond pull test can measure the tensile strength of a wire bond or ribbon bond, a ball shear test can analyse the ball bond, thermal cycling can assess durability by subjecting them to different temperatures, and stress testing can evaluate the wire bond’s thermal endurance and mechanical stress over time.
Capacitive testing is a new approach that leverages the coupling characteristics between metallic surfaces, such as the wire bonds and the metallic plate, also known as the sensor plate above the IC.
This setup effectively transforms each pin and wire bond of the IC into a conductive plate of the capacitor.
It allows for the detection of defects previously invisible to conventional ATE and X-ray methods, such as “near-shorts” between wire bonds and inner leads, as well as vertical sagging wires.
Additionally, capacitive testing can identify issues like incorrect dies and mold compounds.
Principles of capacitive testing
This approach involves transferring electrical energy between two conductors through a shared electric field rather than a direct electrical connection.
This allows for communication or signal transfer between components that are not physically connected by wires.
This concept can be applied in wire bond testing by measuring the capacitance between two conductive surfaces: a capacitive structure above the wire bond area and the wire bond-associated conductive path.
By analysing the capacitive response from the conductive surfaces, the condition and positioning of wire bonds within encapsulated ICs can be evaluated.
Shown in figure 1 above, the Vectorless Test Enhanced Probe (VTEP) is an example which enables this type of testing.
The probe employs advanced capacitive and inductive sensing techniques to detect and measure the electrical characteristics of components and interconnections on a printed circuit board (PCB).
Unlike traditional testing methods that require detailed input-output vectors, this technology can operate without these vectors and offers excellent signal-to-noise characteristics.
Figure 2: Cross-sectional view of a Quad-Flat Package (QFP) wire bond test setup using VTEP
As shown in figure 2 above, the solution utilises advanced capacitive and inductive sensing techniques to detect and measure the wire bond capacitance value.
This process involves injecting the stimulus via the guard pins into the lead frame, which then travels to the wire bond.
When the amplifier touches down on the sensor plate (a capacitive structure in this case), it completes the circuit and picks up the coupling response.
With this approach, the Electrical Structural Tester (EST) leverages advanced capacitive and inductive sensing techniques and part average test (PAT) statistical algorithms in order to learn the baseline wire bond testing from a set of known good units.
Figure 3: “Near short” defect caught with s8050 EST and verified under x-ray
This enables the user to capture any wire bond inflections as outliers, such as the near-short defect caught by the tester in figure 3 above.
Advantages and limitations of capacitive-based testing
The capacitive test methodology is particularly effective for peripheral lead arrangement packages because the leads are positioned next to each other on the same side or surrounding the IC.
Common examples include Dual In-line Package (DIP) and Quad-Flat Package (QFP).
In these, all leads are positioned adjacent to each other or around the perimeter of the IC package.
These packages result in a single layer of wire bonds arranged around the chip rather than stacked on top of each other.
This configuration makes measuring the capacitive coupling signals for determining the physical location of the wire bonds relatively easy and precise.
However, due to technological advancements and the increased complexity of ICs, more advanced packaging types have emerged, such as the Ball Grid Array (BGA) which involves multi-layer wire bond stacking.
Figure 4: Top view of Ball Grid Array (BGA) package
This advanced method presents additional challenges for measuring capacitive coupling signals due to the more complex arrangements of wire bonds as shown in figure 4 above.
The capacitive coupling method may not be suitable for these advanced types of IC packaging.
For example, the BGA arranges its wire bond pads in concentric rings around the chip and on the PCB, resulting in multiple overlapping layers of wires.
This configuration makes measuring the capacitive coupling signal more challenging, as it affects the strength and the signal-to-noise ratio as identified in figure 5.
Figure 5: Cross-sectional view of BGA package with multiple wires overlapping each other
Therefore, it is important to consider the arrangement of the wire bonds before choosing the capacitive coupling test method.
Advanced packaging types with complex wire bond arrangements may require alternative testing approaches to ensure accurate measurements and the reliable detection of defects.
Transforming wire bond defect screening for microelectronics
Wire bonding is pivotal in microelectronics, and with market growth projections soaring, the need for efficient testing methods is greater than ever.
While traditional AXI and ATE systems offer valuable insights, they also have major limitations.
Different types of wire bond deformation defects occur in ICs, and various systems cater to each one of them.
ATE systems can easily detect electrical defects such as opened, shorted, and missing wire defects.
These systems are ideal in high-production settings.
However, they only test electrical defects and fail to detect other issues such as extra or stray wires, near-short sagging or sweeping wires.
As a result, an IC can appear to be fully functional during ATE tests while in fact it may not be.
In contrast, AXI can detect all wire bond defects.
However, this method requires manual visual inspection, which is labour-intensive and prone to human errors.
It is also impractical to screen every batch of IC packages in high-production environments because this would create a bottleneck.
Instead, only a handful of samples can be randomly screened, limiting the effectiveness of AXI for comprehensive defect detection.
Capacitive-based testing addresses both challenges.
This advanced technology enables the detection of previously invisible defects to conventional ATE and X-ray systems, including “near-shorts” between wire bonds and inner leads and vertical sagging wires.
Additionally, it can identify issues such as incorrect dies and mold compounds, expanding its diagnostic capabilities.
When paired with PAT statistical analysis, this type of testing can easily detect electrical and non-electrical defects with a high-test throughput and cope with high production beat rates.
Tech Focus: Breaking New Ground in Wire Bond Inspection with Capacitive Test Methods
Wire bonding is widely used in electronic devices, the semiconductor industry, and microelectronics. Shawn Lee at Keysight Technologies shares why testing wire bonds is not just about ensuring reliability and reducing production costs but also about guaranteeing compliance with industry standards.
Figure 1: Keysight’s Vectorless Test Enhanced Probe (VTEP)
The semiconductor and electronics manufacturing markets are continuing to expand.
A recent report by Fortune Business Insights predicted that the semiconductor market will grow to be worth over US$2,062.59 billion by 2032.
As demand continues to increase, the importance of testing wire bonds grows in parallel.
Wire bonding is widely used in electronic devices, the semiconductor industry, and microelectronics.
It enables interconnections between the die and other electronic components in an integrated circuit (IC), such as transistors and resistors.
Wire bonding establishes an electrical connection between a chip’s bond pad and a corresponding pad on the package substrate or another chip.
Any defects in these bonds can lead to issues like open or short circuits, significantly impacting device functionality.
Therefore, testing wire bonds is not just about ensuring reliability and reducing production costs but also about guaranteeing compliance with industry standards.
Above are some of the common defects that impact wire bonds.
Overview of testing methods
The most widely adopted methods for testing wire bond defects are optical/X-ray inspection using automated X-ray inspection (AXI) and electrical test methods using automated test equipment (ATE).
AXI uses X-rays to penetrate and capture detailed images of wire bonds, detecting hidden defects such as foreign material, voids, and sealing issues.
It is non-destructive and excellent for inspecting complex assemblies.
However, it can be slow and costly, and there are concerns regarding radiation safety.
About the Author: Shawn Lee is product manager for Electronic Industrial Solutions Group at Keysight Technologies.
On the other hand, ATE tests the electrical characteristics of wire bonds, identifying concerns such as open circuits, short circuits, and degraded performance.
It is fast, consistent, and programmable, ideal for high-volume production, but may not detect structural and mechanical defects.
Apart from the electrical and optical test methods, other techniques can be deployed to evaluate the wire bond.
For example, a wire and bond pull test can measure the tensile strength of a wire bond or ribbon bond, a ball shear test can analyse the ball bond, thermal cycling can assess durability by subjecting them to different temperatures, and stress testing can evaluate the wire bond’s thermal endurance and mechanical stress over time.
Capacitive testing is a new approach that leverages the coupling characteristics between metallic surfaces, such as the wire bonds and the metallic plate, also known as the sensor plate above the IC.
This setup effectively transforms each pin and wire bond of the IC into a conductive plate of the capacitor.
It allows for the detection of defects previously invisible to conventional ATE and X-ray methods, such as “near-shorts” between wire bonds and inner leads, as well as vertical sagging wires.
Additionally, capacitive testing can identify issues like incorrect dies and mold compounds.
Principles of capacitive testing
This approach involves transferring electrical energy between two conductors through a shared electric field rather than a direct electrical connection.
This allows for communication or signal transfer between components that are not physically connected by wires.
This concept can be applied in wire bond testing by measuring the capacitance between two conductive surfaces: a capacitive structure above the wire bond area and the wire bond-associated conductive path.
By analysing the capacitive response from the conductive surfaces, the condition and positioning of wire bonds within encapsulated ICs can be evaluated.
Shown in figure 1 above, the Vectorless Test Enhanced Probe (VTEP) is an example which enables this type of testing.
The probe employs advanced capacitive and inductive sensing techniques to detect and measure the electrical characteristics of components and interconnections on a printed circuit board (PCB).
Unlike traditional testing methods that require detailed input-output vectors, this technology can operate without these vectors and offers excellent signal-to-noise characteristics.
Figure 2: Cross-sectional view of a Quad-Flat Package (QFP) wire bond test setup using VTEP
As shown in figure 2 above, the solution utilises advanced capacitive and inductive sensing techniques to detect and measure the wire bond capacitance value.
This process involves injecting the stimulus via the guard pins into the lead frame, which then travels to the wire bond.
When the amplifier touches down on the sensor plate (a capacitive structure in this case), it completes the circuit and picks up the coupling response.
With this approach, the Electrical Structural Tester (EST) leverages advanced capacitive and inductive sensing techniques and part average test (PAT) statistical algorithms in order to learn the baseline wire bond testing from a set of known good units.
Figure 3: “Near short” defect caught with s8050 EST and verified under x-ray
This enables the user to capture any wire bond inflections as outliers, such as the near-short defect caught by the tester in figure 3 above.
Advantages and limitations of capacitive-based testing
The capacitive test methodology is particularly effective for peripheral lead arrangement packages because the leads are positioned next to each other on the same side or surrounding the IC.
Common examples include Dual In-line Package (DIP) and Quad-Flat Package (QFP).
In these, all leads are positioned adjacent to each other or around the perimeter of the IC package.
These packages result in a single layer of wire bonds arranged around the chip rather than stacked on top of each other.
This configuration makes measuring the capacitive coupling signals for determining the physical location of the wire bonds relatively easy and precise.
However, due to technological advancements and the increased complexity of ICs, more advanced packaging types have emerged, such as the Ball Grid Array (BGA) which involves multi-layer wire bond stacking.
Figure 4: Top view of Ball Grid Array (BGA) package
This advanced method presents additional challenges for measuring capacitive coupling signals due to the more complex arrangements of wire bonds as shown in figure 4 above.
The capacitive coupling method may not be suitable for these advanced types of IC packaging.
For example, the BGA arranges its wire bond pads in concentric rings around the chip and on the PCB, resulting in multiple overlapping layers of wires.
This configuration makes measuring the capacitive coupling signal more challenging, as it affects the strength and the signal-to-noise ratio as identified in figure 5.
Figure 5: Cross-sectional view of BGA package with multiple wires overlapping each other
Therefore, it is important to consider the arrangement of the wire bonds before choosing the capacitive coupling test method.
Advanced packaging types with complex wire bond arrangements may require alternative testing approaches to ensure accurate measurements and the reliable detection of defects.
Transforming wire bond defect screening for microelectronics
Wire bonding is pivotal in microelectronics, and with market growth projections soaring, the need for efficient testing methods is greater than ever.
While traditional AXI and ATE systems offer valuable insights, they also have major limitations.
Different types of wire bond deformation defects occur in ICs, and various systems cater to each one of them.
ATE systems can easily detect electrical defects such as opened, shorted, and missing wire defects.
These systems are ideal in high-production settings.
However, they only test electrical defects and fail to detect other issues such as extra or stray wires, near-short sagging or sweeping wires.
As a result, an IC can appear to be fully functional during ATE tests while in fact it may not be.
In contrast, AXI can detect all wire bond defects.
However, this method requires manual visual inspection, which is labour-intensive and prone to human errors.
It is also impractical to screen every batch of IC packages in high-production environments because this would create a bottleneck.
Instead, only a handful of samples can be randomly screened, limiting the effectiveness of AXI for comprehensive defect detection.
Capacitive-based testing addresses both challenges.
This advanced technology enables the detection of previously invisible defects to conventional ATE and X-ray systems, including “near-shorts” between wire bonds and inner leads and vertical sagging wires.
Additionally, it can identify issues such as incorrect dies and mold compounds, expanding its diagnostic capabilities.
When paired with PAT statistical analysis, this type of testing can easily detect electrical and non-electrical defects with a high-test throughput and cope with high production beat rates.
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