Inspecting and Analyzing Printed Circuit Boards Quickly and Reliably with a Digital Microscope

DeRose, James; Schlaffer, Georg

January 11, 2016 Story

Inspecting and Analyzing Printed Circuit Boards Quickly and Reliably with a Digital Microscope

For the past several years, digital microscopy has been shown to be useful for inspection, quality control and assurance (QC/QA), and failure analysis (FA) in the microelectronics industry, especially for printed circuit boards (PCBs). Recently, state-of-the-art improvements have made digital microscopy even more powerful and practical for inspection, leading to a more efficient workflow. Here, the advantages of certain digital microscope features, i.e., intuitive software for operation and analysis, fast and easy ways to change magnification, and encoding for reliable recall of parameters, are explained.

Authors

¹Leica Microsystems

Why Inspection with a Digital Microscope?

Digital microscopes are optical microscopes operated without eyepieces; the image is observed directly on an electronic display. The Leica
DVM6 digital microscope provides users with an even easier and more rapid way to record high quality, reliable image data and make quick
analysis leading to greater efficiency when inspecting microelectronic parts.

Which Features of a Digital Microscope Lead to Reliable Analysis and Greater Workflow Efficiency?

Multiple features of the Leica DVM6 make it easy to use and render the inspection and analysis workflow more efficient:

Intuitive software for microscope operation and data analysis;
Efficient, simple way to change magnification over the entire range (12 : 1 to 2,350 : 1);
Encoding (automated tracking and storing) of important parameters, e.g., stage, optics, illumination, and camera settings, for rapid recall at any time;
Fast and easy microscope head tilting and sample rotation;
Integrated LED (light-emitting diode) ring light and coaxial illumination allowing versatile contrast;
High performance digital camera with fast live image and 10 MP resolution; and
Software enabled/supported capture modes, e.g. XY and XYZ stitching and high-dynamic-range (HDR) etc.

This report discusses how the first 3 points above contribute to a faster, more reliable workflow. For more detail on the latter four aspects please refer to this article on fast and reliable inspection of PCBs.

Quick and easy to setup and get started

Operation of the Leica DVM6 digital microscope only requires a power cable and a USB cable connected to a computer running the Leica Application Suite X (LAS X) software. Once an objective lens is in place, the Leica DVM6 is ready to perform inspection, QC/QA, and FA. The maximum working distance is 60 mm, the sample stage travel range is 70 × 50 mm, and the maximum sample weight is 2 kg.

Below is a photo of the Leica DVM6 digital microscope with a PCB (printed circuit board) placed onto its stage, as well as a photo of the PCB, and a low magnification DVM6 image of a region of it.

Figure 1: Leica DVM6 digital microscope with PCB (printed circuit board) sample on stage.

Figure 2: Printed circuit board (PCB) used as sample.

Figure 3: Low magnification image of a part of the PCB sample recorded with the Leica DVM6.

Measurement, analysis, and operation with intuitive software

In order to achieve a faster and reliable workflow for inspection, QC, and FA with a digital microscope, an intuitive software package with numerous functions for microscope control, simple yet flexible image acquisition, and sample analysis is essential. For example, the software used with the Leica DVM6, Leica Application Suite X (LAS X), offers storage of multiple user profiles for cases where many different users work with the same microscope. The Z-stack function of LAS X enables users to record images in various focal planes over a defined Z-range for a sample feature or the entire sample itself. The extended depth of field (EDOF) mode provides a multi-focus image without the need to set begin nor end levels. Both Z-stack and EDOF allow the fast creation and analysis of 3D topographic surfaces [1] of a sample.

In addition, with LAS X software, users can choose different modes for a large XY scan, such as "mark & find", "tile scan", and "spiral scan". An interactive mode called "Live Image Builder" for XY (2D image), Z (3D image), and XYZ (3D image over extended area) can also be used.

Examples of 3D sample analysis using LAS X are shown below with a PCB (printed circuit board) and SMD (surface mounted device) hybrid sample. Report generation with just one click is also explained.

3D image of a portion of a PCB showing integrated circuit (IC) chips and a solder joint; captured with a Leica DVM6 using the EDOF (extended depth of field) function of LAS X. See also same image on the right with color Z-scale. — Figure 4: 3D image of a portion of a PCB showing integrated circuit (IC) chips and a solder joint; captured with a Leica DVM6 using the EDOF (extended depth of field) function of LAS X. See also same image below with color Z-scale.

Figure 5: Same 3D image as above with color Z-scale.

2D image of part of a PCB showing a capacitor and a bit of an IC chip. Captured with a Leica DVM6 using EDOF. See on the right the 3D image of this PCB region. — Figure 6: 2D image of part of a PCB showing a capacitor and a bit of an IC chip. Captured with a Leica DVM6 using EDOF. See below the 3D image of this PCB region.

Figure 7: 2D image of part of an SMD hybrid with transistors or diodes. Captured with a Leica DVM6 using EDOF.

Figure 9: 3D image of the SMD part shown above. Various measurements, such as profile, step height, and volume, have been made.

Figure 10: 2D image of part of a PCB showing an IC chip and a capacitor. Captured with a Leica DVM6 using EDOF. See below the 3D image of this PCB region.

3D image of PCB region. Measurements of area, volume, step height, length, etc. have been made. A report is created as an excel file by clicking “export” (marked by the yellow box). — Figure 11: 3D image of the PCB region shown above. Measurements of area, volume, step height, length, etc. have been made. A report is created as an excel file by clicking “export” (marked by the yellow box).

Figure 12: Created report from measurements: summary tab of excel file showing 1st page of report with 2D image of PCB region.

Figure 13: Created report from measurements: image tab of excel file showing measurements and 3D image of PCB region.

Fast magnification change over a large range

The objective lenses of the Leica DVM6 are quickly and easily changed during operation of the instrument with essentially no increase in workflow. This online video shows how simple it is to switch objectives [2].

There is a selection of 3 plan apochromatic (chromatic correction over the red, green, and blue wavelengths and flatness correction over the whole field of view) objectives (low, middle, and high magnification). There is also the 16 : 1 integrated zoom optics with which users can achieve total magnification values from 12 : 1 to 2,350 : 1 (with the recommended 27 inch (69 cm) diagonal monitor display in accordance with the standard ISO/DIN 18221) [3]. The zoom optics works with each of the 3 objectives for low, middle, and high magnification, making it possible to change the magnification in a continuous manner over the full range.

It must be kept in mind that the final magnification value for digital microscopy will depend on the monitor size used for image display [3]. As mentioned above, it is recommended that the Leica DVM6 be operated with a 27 inch (69 cm) diagonal monitor. Images of an electronic sensor acquired with the Leica DVM6 using the low, middle, and high objective at low, middle, and high magnification are shown below.

Figure 14: Leica DVM6 image of an electronic sensor: low magnification range (low objective).

Figure 15: Leica DVM6 image of an electronic sensor: middle magnification range (middle objective).

Figure 16: Leica DVM6 image of an electronic sensor: high magnfication range (high objective).

Encoded parameters of the Leica DVM6 digital microscope

An instrument with hardware in direct communication with computer software to allow the automatic tracking and saving of specific parameters is called an "encoded" device. Encoding is very useful for rapidly recalling parameters and settings stored during data acquisition. Encoding is invaluable for reproducibility and reliability and also contributes to a more efficient workflow.

For the Leica DVM6, the objective and zoom optics, camera pixel resolution, sample stage position and rotation angle (whether manual or motorized movement), microscope head tilt angle, and illumination system settings are encoded and stored via LAS X software. An example of the encoding of some of these parameters during operation of the Leica DVM6 is shown below.

Figure 17: Operation panel of LAS X for the Leica DVM6. The total magnification value (19x, <2.00> is the zoom factor) from objective and zoom optics, microscope head tilting angle (5°), and stage rotation angle (20°) are encoded. The same parameters are also displayed in the lower right corner.

Lower right corner of LAS X panel above. The field of view (FOV) or object field (marked by the green rectangle in the images above) is also encoded (objective and zoom optics). — Figure 18: Lower right corner of LAS X panel above. The field of view (FOV) or object field is also encoded (objective and zoom optics).

Conclusions

More efficient, reliable inspection, quality control and assurance (QA/QC), and failure analysis (FA) for microelectronics parts, such as printed circuit boards (PCBs), is achieved with the Leica DVM6 digital microscope. Here three of its benefits were discussed: intuitive software with many functions for microscope operation, image capture, and data analysis; convenient ways to change magnification rapidly over the full range from 12 : 1 up to 2,350 : 1; and encoding of all important parameters and settings (optics, camera, stage, head, and illumination) for easy, fast recall. These features allow Leica DVM6 users to make faster and reliable data acquisition and analysis for greater inspection, QC, and FA workflow efficiency.