3D TOPOGRAPHY & IMAGE OVERLAY OF PRINTED CIRCUIT BOARD ASSEMBLY

Transcription

1 3D TOPOGRAPHY & IMAGE OVERLAY OF PRINTED CIRCUIT BOARD ASSEMBLY Prepared by Duanjie Li, PhD & Andrea Novitsky 6 Morgan, Ste156, Irvine CA P: F: nanovea.com Today's standard for tomorrow's materials NANOVEA 1

2 INTRO Printed circuit boards (PCB) are commonly used on electronic devices such as phones, radios, radar and computer systems. The circuits of the PCB are formed by laminating and etching a thin conductive layer of material onto a non-conductive substrate. Individual electronic components are supported and connected by the conductive circuits on the PCB. As the electronic devices develop towards miniaturization, multifunction and higher speeds, the demands for complex circuit patterns with high density of small electrical components increases tremendously. IMPORTANCE OF 3D NON-CONTACT PROFILOMETER FOR PCB ASSEMBLY INSPECTION The more sophisticated electronic design and layout of semiconductor chips, circuits and systems requires high precision manufacturing and superior quality control. Unlike other techniques such as touch probes or interferometry, the Nanovea 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any material surface. Nano through macro range is obtained during surface profile measurement with zero influence from sample reflectivity, absorption and high surface angles. This is ideal for surface inspection of the PCB assembly (PCBA), which contains a variety of electronic components of different materials, reflectivity and fine features. Moreover, the non-contact profiling technique measures the surface features without touching the PCBA, avoiding the risk of damaging the delicate circuits and electronic components due to sliding of the probe stylus. The combination of high precision, high speed, non-contact and user friendliness makes the Nanovea Profilometer an ideal tool for PCBA inspection. MEASUREMENT OBJECTIVE In this application, we showcase that the Nanovea ST400 Profilometer equipped with an optical microscope provides fast and precise 3D profile measurement and comprehensive indepth analysis of a PCBA. Figure 1: Integrated optical microscope mapping on the PCBA. 2

3 RESULTS AND DISCUSSION An array of 4 4 microimages were automatically taken and stitches as shown in Figure 2a, in order to obtain a better observation of the area on the PCBA for inspection under the microscope. This is followed by high precision 3D surface scan at the selected area of interest. Figure 2b and c shows the optical image and the surface topography at the area selected for 3D scan. (a) (b) (c) Figure 2: Select an area for 3D topography measurement on the optical image. 3

4 The 3D View provide users a tool to directly observe the PCBA from different angles and magnifications by rotating and zooming-in the 3D image as shown in Figure 3. The Nanovea analysis software overlays the optical image on the 3D topography. It allows users to correlate the surface features observed under the microscope to the 3D profile of the PCBA and reveals more details such as surface material, texture and patterns compared to the false color 3D topography. Figure 3: Overlay of the surface topography with the optical image. Figure 4 shows the 3D view of the microchip under a higher magnification to display the 3D topography of the microchip in details. The microchip was scanned using a high resolution (Figure 4a) and a low resolution (Figure 4b) for comparison. It is evident that the microchip at a higher resolution exhibits much more surface features. Such a detailed scan enables close inspection of the PCBA surfaces at a micro level to detect possible local defects and flaws of the electronic components and circuits. In comparison, the lower resolution scan provides a blurry look of the surface. The overlay of the surface topography with the optical image can provide an overall direct look of the surface features; however, the high resolution 3D scan provided by Nanovea Profilometer using axial chromatism technique can reveal the detailed true topography of the scanned surface with a high precision. It is not limited by the resolution of the optical image. The white light axial chromatism technology measures height directly from the detection of 4

5 the wavelength that hits the surface of the sample in focus with no mathematical software manipulation. (a) High resolution topography: (b) Low resolution topography: Figure 4: (a) High resolution and (b) Low resolution 3D views of the chip on the PCBA. The surface features can be quantified in numerous ways using built-in software tools as shown in the following figures as examples. Figure 5 shows the 2D profile of the microchip. It can be observed that the chip has a thickness of µm. µm L1 R1 L2 R2L3 R mm Parameters Unit Step 1 Step 2 Step 3 Maximum height µm Mean height µm Figure 5: Profile extraction and amplitude parameters of the chip. 5

6 The electronic circuit of the PCBA is inspected using the Contour Analysis as shown in Figure 6. Since the electronic circuit is composed of individual electronic components connected by conductive wires or traces, the size and plan of the circuits is critical to ensure proper electric current flow. Such contour analysis provides an ideal tool for quality control and R&D of the PCBA. mm mm R mm mm mm mm mm mm mm R mm R mm mm mm mm CONCLUSION mm Figure 1: Contour analysis of the PCBA. In this application, we have shown that Nanovea 3D Non-Contact Profilometer equipped with an optical microscope is an ideal tool for PCBA inspection. The automatic microscope image array enables better observation of a larger surface under the microscope. The area of interest for 3D scan can be directly selected on the optical image array, which substantially reduce the time on 3D surface measurement. The overlay of the optical image and 3D topography allows correlation of the surface features observed under the microscope to the 3D profile and better detection of the defects on the PCBA. The data shown here represents only a portion of the calculations available in the analysis software. Nanovea Profilometers measure virtually any surface in fields including Semiconductor, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others. Learn more about the Nanovea Profilometer or Lab Services 6

7 APPENDIX: MEASUREMENT PRINCIPLE The axial chromatism technique uses a white light source, where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will vary in relation to the wavelength of the light. In effect, each separate wavelength of the incident white light will re-focus at a different distance from the lens (different height). When the measured sample is within the range of possible heights, a single monochromatic point will be focalized to form the image. Due to the confocal configuration of the system, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus. The spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of CCD, which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position. Unlike the errors caused by probe contact or the manipulative Interferometry technique, White light Axial Chromatism technology measures height directly from the detection of the wavelength that hits the surface of the sample in focus. It is a direct measurement with no mathematical software manipulation. This provides unmatched accuracy on the surface measured because a data point is either measured accurately without software interpretation or not at all. The software completes the unmeasured point but the user is fully aware of it and can have confidence that there are no hidden artifacts created by software guessing. Nanovea optical pens have zero influence from sample reflectivity or absorption. Variations require no sample preparation and have advanced ability to measure high surface angles. Capable of large Z measurement ranges. Measure any material: transparent/opaque, specular/diffusive or polished/rough. 7