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High Resolution Optical Inspection Solutions
Ultra 850G with mag handlers.
By Paul Groome, Machine Vision Products, Inc., Carlsbad, CA
As electronic systems get smaller, the division between semiconductor and SMT manufacturing is blurring. For microelectronics inspection the opposite is happening. The division between AOI manufacturers is becoming more defined with only the highest quality AOI manufacturers being able to meet the higher accuracy, repeatability and measurement requirements.
MVP's tools cover the back-end semiconductor processes: epoxy, underfill, wire bond, part height, dimensional measurements and SMT.In addition, due to component density (breaking most IPC rules) and the small size of components and dies, the measurement of placement accuracy is essential to maximize yields and reduce field failures.
The company is providing solutions to meet the future needs of microelectronics manufacturing with its metrology-based Ultra 850G platform.
(Left: correctly placed die; (right) incorrectly placed, partially rotated die.
When working with microelectronics products, the number of sensors/tools — AOI and 3D — available are the most important aspects of the inspection system. Each tool needs to have the capability of performing measurements and provide accurate feedback to the process. To ensure the correct manufacture of these parts MVP provides a class-leading toolbox of inspection techniques. The Ultra 850G Automated Microelectronics Inspection System can provide high accuracy solder, silver epoxy, underfill, wires, wire bonds, die, substrate, "x", "y" and "z" dimensional measurements.
The inspection needs, in turn, highlight the need for multiple sensors, high resolution AOI metrology and 3D laser height measurements, in the same platform. MVP provides the ability to use all measurement techniques at the same time. This allows for full inspection of microelectronics on the same system.
Higher resolutions are required to provide full inspection of smaller features such as wire bonds. Resolution is normally the only issue that an inexperienced AOI manufacturer wants to discuss; but the repeatability and accuracy are just as important. The design of a microelectronics inspection system needs to encompass all of these items.
Ambient temperature can be a problem; if there is a one degree F temperature increase, the AOI imaging gantry, when built from aluminum, will expand 0.013mils (0.33µm) per inch (25.4mm).
So in a factory where the temperature could change between 65 and 75°F (18.3 to 23.9°C) the error could be as high as 0.65mils (15.5µm) across a 5-in. (127mm) substrate if the system has not been designed correctly to minimize these effects.
In turn a granite stage with a thermal expansion coefficient of 0.004mils per inch (0.1016µm per 25.4mm) will have 1/3 of that error at 0.22 mils (5.588µm) across the same 5-in. (127mm) substrate.
The system also needs to be designed to minimize the effects of vibration; at 1µm resolution, the smallest vibration will substantially reduce the repeatability and capabilities of a system. Temperature variations and vibration are both accommodated in the Ultra 850G platform, which is designed to provide the highest resolution while still providing the highest repeatability in a system that is intended for microelectronics inspection.
Multiple issues arise from die placement that requires the use of 3D and 2D measurement capabilities. For example defect modes include:
Edge cracks from dicing.
Placement vs. bump pad position.
Underfill tongue, flow, spread, rollover.
It is key for an inspection system to provide flexible lighting configurations for the many different finished die surfaces and defect types associated with a die. The 3D lighting configurations used allow for the highest contrast between die edges and the substrate, while still being able to highlight foreign material, cracks and chips on the die.
Comparison of 5mil aluminum wedge bond seen with standard hi-res AOI system (lower right) and 1um resolution.
The 3D laser solution also provides for the measurement of die tilt. Measuring the variation of the die corner heights with reference to the substrate is straightforward. This allows for measurement of the material volumes between the die and substrate to locate possible cure/volume issues.
The biggest loss of yield is normally associated with die placement errors. These errors normally arise from placement accuracy and thermal expansion of the die and substrates. To ensure the highest yields in a die placement process accurately measuring the die position and ensuring correct placement is key. MVP provides the highest accuracy when measuring die placement, with all data and offsets being available to other parts of the process to allow corrective actions to be taken. Measurement studies have shown repeatability below 2µm.
All die and epoxy processes can be fully measured, defects analyzed and data reported for full SPC and process control.
Resolution and repeatability are the number one requirement to ensure accurate measurement on wire bonds. For comparison, the example below shows a 5mil (127µm) aluminum wedge bond that has been imaged on the Ultra 850G and a High Resolution AOI system. The AOI system used for comparison has resolution used for standard SMT inspection of components down to 01005 size. The results are dramatic with a 10X increase in resolution allowing MVP to provide full inspection on bond and wire.
If we now look at 1mil (25.4µm) gold wires, MVP provides inspection on the ball/crescent bond and wire, measuring for the presence of the wire, and bond area, providing measurement data allowing for defect location and process control.
As the position of wire bonded die will vary across a substrate, the Ultra 850G deploys proprietary algorithms to locate each die/substrate and references the wire bond positions to each unique die. Without this capability, wire inspection would not be viable.
Algorithms also need to vary across ball, wedge, crescent and tape bond processes. The company provides capabilities for all bond types. Wedge bonds and ball bonds are fully inspected. The system also provides the capability of inspecting the bond at the crescent end of a gold wire, not only inspecting the wire, but also providing full measurements.
In wire bond processes, it is important to measure surface quality before the bonding process, to discover any foreign materials and solder splatter on the bond pad — locating them before the bonding process. The capability to detect these defects can remove costly latent problems where bonds may not have the needed integrity because of solder splatter or foreign materials on the bond pad.
When the Ultra 850G's resolution and repeatability are combined with the company's unique die/bond location algorithms, the system is able to provide vastly superior capabilities to the microelectronics manufacturer.
Bump and Co-planarity
Because of the ability to use multiple measurement technologies in the same system, the Ultra 850G provides full capabilities after the bumping process. The inspection includes ball/bump position, diameter, shape and height. These are all measured in real time with optical and 3D data being measured in the same inspection. The patented 3D measurement technology uses a high-speed scanning technique that allows height measurements at line rates.
Now consider the SMT components used in microelectronics products. In most cases these are the same format components as used in conventional SMT manufacturing. However, one of the major differences on many microelectronic substrates: the IPC610 minimum spacing rules are commonly broken. This drives the need for accurate placement metrology, trend analysis and closed loop feedback to the placement process. In some cases component spacing on these substrates can be below 100µm, so any translation errors can cause catastrophic defects and need to be caught as early in the process as possible.
Multiple measurement technologies in the same system providing ball/bump position, diameter, shape and height measured in real time in 3D.
MVP provides enhanced edge-finding algorithms that accurately locate component edges to calculate the exact offset vs. pad location for each component and enable real-time monitoring of the placement and cure processes. As bonding agents like Silver Epoxy are used in place of solders, full capability is provided to measure both solder and silvered epoxy deposits.
In conclusion, it is important to remember that no matter how high the resolution, no matter how good the camera, the system must be correctly positioned on a repeatable basis, and it must be able to account for external variables. A microelectronics inspection system is a high accuracy optical/3D inspection system that provides the accuracy and repeatability required for microelectronics. The Ultra 850G system is designed to provide accuracy and stability in spite of such external variances as temperature and vibration.
A microelectronics inspection system has to be designed to provide the high resolution that is required for microelectronic devices and measurements. The system also requires an extensive measurement toolbox to provide the measurements that are required for high quality manufacturing processes. Put these all together, and you have a system that does the job — and then some.
Contact: Machine Vision Products, Inc., 5940 Darwin Ct., Carlsbad, CA 92008
800-260-4687 or 760-438-1138 fax: 760-438-0660 E-mail: email@example.com Web:
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