While available microscopes range from low-priced microscopes with low power and simple objectives to scanning electron microscopes that can take up a large-sized room, in industry the three most common tools are stereo microscopes, compound microscopes and hybrid measuring microscopes.

A stereo microscope is a general inspection microscope that allows users to look at parts in 3-D. It shows the part as an upright and real image and has magnification ranges from 5X to 400X. It has low power, but a lot of working distance so it can manipulate parts under the lens, and a zoom optical system allows the microscope to go from low magnification to medium magnification as needed. This is particularly useful when assembling parts, especially small components, says Michael Metzger, department manager, measuring instruments, Nikon Instruments (Melville, NY).

“Stereo is the most popular microscope in the industry,” says Metzger, “This is partly because it is easy to use and has a lot of general uses to it. It is also because it is the least expensive.”

A compound microscope is popular for use by manufacturers who make small products such as electrical parts, photonics and semiconductor devices. “All high-end electronics demand higher magnification, so the high power of the compound industrial microscope magnification can go all the way up to 1,000X to 1,500X,” says Metzger.

Compound microscopes typically do not use zooming optics, instead they used a fixed, objective lens, which is the lens closest to the part, that has a turret of objective lens’ of varying magnifications mounted in a rotating nosepiece. The fixed lens produces a more precise image than a zoom lens. This is important because any distortion may cause the part to be evaluated incorrectly.

Its biggest feature is its ability to do advanced contrasting techniques such as bright field, dark field, polarized light and differential interference contrast. These techniques are designed to help the operator see part features that are typically difficult to view because of low contrast, such as a contact lens submerged in a solution.

Another example is a cross section of a laminated surface that may have layers of plastic, paint and metal. In typical microscopy, the laminated surface would be mounted in a potted sample and cut in half. The edge would be polished to show all the layers from a cross point of view. However, these surfaces often tend to be difficult to distinguish from one another so the use of advanced contrasting techniques is required.

A measuring microscope is a hybrid of a compound and stereo microscope that features a precise measuring platform. It can be assembled with some of the features of the stereomicroscope, such as a long working distance or zoom optics, or it can be assembled to be more of a compound microscope with a turret of fixed lenses.

“A measuring microscope can perform two operations,” says Metzger. “This flexibility helps to reduce costs and increase throughput.”

For instance, Metzger says a photonics’ device application typically requires precise measurements that fixed lenses offer and high magnification that a compound microscope might provide to see the components that are mounted on a silicon substrate.

Why not video?

However, even video systems are not as good as the human eye, according to Metzger. “Human eyes are sometimes needed to make that very fine determination,” he says. “Typically, what happens is people buy vision systems and think that they will measure everything automatically, but at times images may have strange optical effects, reflected images or anomalies. The vision system can become confused and measure incorrectly.”

A solution to these potential anomalies is the contrasting techniques that microscopes offer that video systems cannot. While many of the contrasting techniques are well known, microscope makers are developing new techniques. Carl Zeiss MicroImaging Inc. (Minneapolis), for instance, has developed new contrasting techniques such as the Deepview technique. Dan King, assistant product manager, materials microscopy for Zeiss, says this method allows users to increase the depth of field of high magnification objectives by up to 20 times. “This means the microscope user no longer has to continuously focus to see all the features of a given sample,” he says. “It puts all planes of focus, both in and out of focus, for a given sample, and combines them into one image. This image is in focus for easy observation in quasi-real time. Only an SEM (scanning electron microscope) had the ability to do this before now.”

Nikon also has developed new products to make its products easier to use. For instance, on its MM40 and MM60 measuring microscopes, the company has installed its newly developed optical Focusing Aid that is meant to take more accurate measurements of the Z-axis. The measuring microscopes also have a linear glass scale that covers the full range of vertical movements, and the two together were designed to improve the reliability of Z-axis measurements.

Digital cameras

In addition, it allows users to document the microscope inspection. King says that this documentation is becoming a vital aspect of using microscopes. Research and development departments for instance, often develop new materials and want to catalog them as they go along.

Traditionally, a microscope user such as a metallurgist who wanted to capture the image would take a Polaroid image in a 4- by 5-inch format. However, King says that that format is being phased out and supplies are limited: “Every picture is like $3 or $4, and if you take a bad photo, you need to take another one. In addition to that, if you take a picture on film, you have to have some place to store it,” he says.

The digital cameras and new software and control boxes are also being implemented to improve microscope use. Vision Engineering (New Milford, CT) has a new Hawk Microscope with PC software that lets users do CAD import and export, custom reporting and CNC control. For more basic data processing, a microprocessor represents X, Y and Z measurements in both numeric and graphic form. Results can also be printed via a parallel printer port. Systems are also available in motorized and fully automated, edge detecting configurations.

The software that drives the cameras on microscopes can clean up images and increase contrast. The sophisticated software can combine field of view measurements and add them together and do analysis.

For instance, Mitutotyo America’s (Aurora, IL) new controller, the QM-Data200, allows users to do field of view measurements, such as diameters of circles and angle measurements.

“You can click on one point and click on another point,” says Walter Wardzala, group manager, precision-measuring instruments, “and the computer will tell you it is 482 pixels. A pixel is 1/4 of a micron, and so it must be that far apart.” Q

TECH TIPS

• Many microscopes are available today, but three are most common: stereo, compound and measuring.
• Digital cameras allow the microscopes to capture images and send them to other locations.
• Field of view measurements can be made with sophisticated new software.