Printed circuit board (PCB) manufacturing continues to steamroll toward smaller, denser packaging to meet the requirements of shrinking electronic products. More sophisticated components such as small-outline ICs, plastic leaded chip carriers, ball-grid arrays (BGAs), and flip chips are smoothing the way.
The smaller devices also present ruts in the road of the inspection process because the defects are more difficult to find. And if that were not enough, customers also expect products to be defect-free.
Inspection-equipment manufacturers are filling in the rough spots with updated methodologies, algorithms, and control techniques to keep output and board quality at optimum levels. For example, inspection systems are available for testing further upstream in the board-fabrication process to achieve continuous improvements in processes, yields, and quality while reducing costs, said Dominic Haigh of Teradyne’s Control Automation Group. With less time for each step of the manufacturing process, the pressure increases to find faults as early as possible to minimize wasted process steps.
One of the trends is toward higher system performance with near-perfect inspection rates, said George Ayoub, president of Machine Vision Products. Manufacturers want false call rates of less than 50 ppm, the flexibility to use the system anywhere in the production line, and an inspection rate that matches the speed of any manufacturing line.
Limited access to densely packaged components is another challenge for inspection systems. PCBs for consumer electronic products, such as laptop computers and cellular phones, are extremely tough to inspect, said Arlene Hagio, product marketing engineer at Hewlett-Packard. Limited access is forcing some PCB manufacturers to look beyond traditional inspection techniques and in-circuit tests for assessing their assembled boards.
Automated X-ray inspection is a valid solution for inspecting dense, complex boards, said Ms. Hagio. However, most X-ray inspection is relegated to the repair-loop, process-development, and process-sampling environments because most cannot keep pace with the cycle times of high-volume board manufacturers. The new HP 5DX Series II Family of X-ray products with 60-s to 90-s cycle times meets the needs of these high-end electronics manufacturers.
While one section of the PCB design industry decreases the board size and increases the density, another section increases the board size and population density, continued Ms. Hagio. Manufacturers of memory and mainframe boards, for example, are designing 18″ × 20″ boards with 50+ BGA components.
Limited access to the components and economic issues related to the size and complexity are major concerns for these companies. Because these boards are very expensive, it is critical to identify the most cost-efficient means of bringing the boards into volume production with the minimum number of prototype runs.
The increased density and complexity of all PCBs also add to their value, and companies are less willing to scrap them, said Jim Walcutt at Compix. These higher- density boards are using flip chips and BGAs which have different problems than boards with older technology, such as quad flat packs. Certain BGA packages develop power to ground shorts during the reflow process when solder tendrils are formed from the pad to the grounded underside of the device.
Unfortunately, the locations of the power to ground shorts are difficult to find during board test, said Mr. Walcutt. Infrared thermography is one method that isolates the problem to the offending BGA. Shorts between inner layers due to poor router performance are more difficult to spot as the amount of resistance at the short is very low and the I2R losses are small and hard to detect.
Small-hole drilling of vias most often handles the increased I/O density, said Gil Zweig, president of Glenbrook Technologies. Smaller vias allow a greater number of signals to be transferred in the same space on the board. Common via hole sizes in production are 0.010″ dia while a 0.006″-dia hole now is used for prototype runs.
Inspecting area-array packages such as the BGAs and flip chips is a significant challenge for inspection, agreed Mr. Zweig. Conventional visual-inspection techniques find it difficult or impossible to verify solder defects or the placement of these new devices because the contacts are hidden from view. X-ray inspection identifies the common BGA assembly defects including solder bridges, missing balls, and misalignment.
The X-ray inspection system refines the assembly parameters such as solder-paste selection, paste thickness, and the reflow oven temperature profile. Once the proper process parameters are developed, X-ray inspection typically is used for spot checks since electrical testing reliably certifies proper assembly.
Whatever inspection technique you use, the sign posts on the road clearly point to equipment that can find faults on smaller components on more densely populated boards and earlier in the process. Applying the appropriate inspection technique at the first possible production step also will save you time and money.
Board Inspection Products
PCB Inspection System Offers
Process-Control Capabilities
The AOI-2500 Series of automated PCB inspection systems transports boards through the inspection cycles, detects artwork and board defects, and provides process-control data. It views PCBs with a minimum line width of 2 mils and detects flaws as small as 0.0004″. The 2500ST checks 18″ × 24″ panels in 3 s or 9,700 panels per shift, and the 2500S performs inspections at a rate of 600 panels per shift. The systems can be used in-line to inspect both sides of PCBs. AOI International, (508) 937-5400.
Thermal Imaging System
Measures to 150°C
The PC2000 is a thermal imaging system comprised of an IR camera, a folding stand, and a card that plugs into the expansion slot of a PC. Temperature measurements can be made from 17°C to 150°C with a resolution of 0.2°C. Images contain 47,000 pixels. Thermal evaluation software is provided. The portable PC2000/e includes an external controller module and connects to the parallel port of a laptop computer. Compix, (503) 639-8496.
Automated X-Ray System Finds
Shorts, Opens, Misalignments
The CRX-2001 BGA Buster™ finds incorrect ball shapes and sizes, missing balls, shorts, opens, and misalignments. The system also verifies chip-packaging interconnects, ultra fine-pitch components, and tape automated bonding. It has a password-protected, Windows® 95-compatible interface, X-ray sources with levels to 160 keV, and focal spot sizes <2 µm. A rotational plate allows the board-under-test to be rotated in three dimensions. Test-results files can be integrated into a production control network. CR Technology, (714) 448-0443.
X-Ray System Offers
10″ FOV, 10 Line Pairs/mm
The B Series of the Model RGX is a reverse-geometry X-ray system offering a laminography option for inspecting each layer of multilayered boards. The X-ray tube has a 10″ and 3″ field-of-view (FOV) and an area magnification from 1 to 100 times. Contrast resolution for plastics and composites is 0.5% and 0.3% for 165-mil thick aluminum. Spatial resolution provides 10 line pairs/mm for 3″ FOV and 4.5 line pairs/mm for 10″ FOV. Included software helps store, enhance, manipulate, and export images. Digiray, (510) 838-1510.
System Provides
Real-Time Imaging on PC
The Tracer™ Thermal Imaging System records and analyzes thermal event sequences at real-time frame rates, up to 60 Hz, on a Windows-based PC. The system includes the company’s Prism DS infrared camera, a Pentium®-based PC, a digital recording system, and software. It records 5+ minutes at a 60-Hz frame rate with 12-bit pixels, capturing 9.3 MB of data/s. The system senses temperature differences of <0.1°C @ 30°C, and measures temperatures from -10°C to +2,000°C with an accuracy of ±2%. FLIR Systems, (503) 684-3731.
Portable X-Ray System
Inspects BGAs
The RTX Mini Real-Time X-Ray System fits on a desktop, is portable, and inspects BGAs, multilayers or leaded components. It has a 16″ × 5″ footprint and weighs 59 lb. The system incorporates the company’s patented X-ray camera that reveals defects as small as 0.001″. Systems may be upgraded with image processors and customized to accept any board. Glenbrook Technologies, (201) 361-8866.
Microscope Features
115-mm Working Distance
The LEICA GZ6T Microscope has a conductive body that provides static protection for inspection and assembly operations of electronic components. Optical features include a 115-mm working distance, 6.7× to 40× magnification, a 360° rotating body, and a one-turn zoom range. The unit also has four banana plugs and two threaded ports for electrostatic grounding of several devices simultaneously. Leica, (800) 248-0123.
Solder-Paste Inspection System
Integrates 3-D Capabilities
The 1820/L Inspection System checks solder paste as well as components on PCBs. An integrated laser adds a 3-D inspection capability to the existing system. The system features a statistical process control package and a user-defined procedure for a variety of inspection needs, including 100% checking of all components in 3-D. Machine Vision Products, (800) 260-4MVP.
Mini Mirror Helps
Inspect BGAs
The Ball Grid Array Mirror helps inspect the outer and inner rows of solder balls of a BGA. The mirror is hand-held or self-standing. It measures 0.754″ L × 0.190″ W. Metron Optics, (619) 755-4477.
Laser-Aiming IR Thermometer
Measures From -50°C to +500°C
The M102L IR MAN® Infrared Thermometer is a laser-aiming, hand-held tool for spot measurements. Temperatures from -50°C to +500°C with 0.1°C-resolution are measured 2 mm from the target. The unit has a built-in memory for 70 readings; a digital output for data download; average, minimum, and maximum readings; field adjustable audible and visual alarms, and 20 h of operation from rechargeable batteries. Mikron Instrument, (800) 631-0176.
Real-Time X-Ray System Has
Variable FOV to 1.6″
The NXR-1400i Real-Time X-Ray Imaging System inspects PCBs, components, and multilayer circuit boards. The X-ray source and detector move independently, providing a magnification range from 4× to 50×, an image area from 0.22″ to 1.60″, and a resolution from 6 lp/mm to 32 lp/mm. The energy source is variable from 20 kV to 120 kV with power settings from 10 W to 62.5 W. Applications include inspection of SMT assemblies, BGAs, gullwings, plated-through-holes, multilayer PCBs, and fine- pitch solder joints. Nicolet Imaging Systems, (619) 635-8600.
X-Ray System Measures
Pads on Inner Layers
The INNERVISION System measures the position of pads on inner layers, reinforcements in gaskets, and encapsulated or laminated features. The measurements and images reveal and quantify offset, skew, stretch, shrink, and distortions that occur on internal details. It features position measurement accuracy to ±10 µm. Operations Technology, (908) 362-6200.
Inspection Machine Analyzes
Solder Paste
The Panasert IPJ-V uses color line-scanner technology for area-calculated solder paste and surface-mount inspection with 30-µm resolution. The automated inspection machine performs in-line quantitative analysis of solder-paste printing and component mounting conditions. It detects blurred, smeared, bridged, misaligned, or missing solder paste as well as missing or misplaced components. Panasonic Factory Automation, (708) 288-4400.
AOI System Collects and
Processes Data in Real Time
The InterScan 5519A+ and B+ Automated Optical Inspection Systems collect and process data in real time. The 5519A+ inspects fine-pitch components of <50-mil pitch with a 0.4" field of view. The 5519B+ checks components ³ 50 mil pitch with a 1″ field of view. The 5519A+ views components from 1 to 2 in.2/s and the 5519B+ from 2 to 3 in.2/s. Applications include inspecting solder bridging, detecting skew, and lead verification on pre- or post-solder processes. Teradyne, (510) 932-6900.
In-Tray Inspection System
Provides Warpage Information
The Model 880-200 In-Tray Lead/Bump Inspection System measures QFP, TQFP, TSOP, BGA, and CSP devices. It provides information on package warpage, regression plane, coplanarity, standoff, ball diameter, and lead angle. The system uses the company’s patented scanning laser technology in conjunction with a 200-MHz Pentium® processor, a PCI-based scan buffer, and imaging hardware to acquire 2-D and 3-D data at >2.4 M data points/s. The laser beam sweeps over the tray with 0.1- to 1.0-micron resolution. Software generates statistical process control information in real time for package and lot summaries, the percentage and number failed, percentage yield, and the number of units inspected per hour. View Engineering, (313) 975-7664.
Microscope Offers
Fatigue-Free Viewing
The COBRA Inspection and Measurement System uses the proprietary Expanded Pupil Viewing (EPV) technology and an ergonomic design to provide fatigue-free viewing with microscopic capabilities. The EPV function helps project ray bundles to the operator’s eyes, widening the field of view and enhancing binocular viewing. The movable eyepieces offer easy head movement in all three planes. The COBRA features patent-pending refractive disk technology and a straight optical path. Vision Engineering, (860) 355-3776.
Video Magnifiers Feature
Constant Focus Lens
The VTEK Spectra Video Magnifier features a lens, a camera, a monitor, and provides multiple video output signals including SVGA, S-Video, and NTSC versions. It is used for assembly, inspection, and training applications. The Spectra offers a 17″ or 21″ monitor and an optional microphone and VCR. It provides brightness and contrast enhancements of parts, records objects, and converts them to electronic form. The Spectra has a variable magnification from 4× to 50× that stays focused even when the magnification is changed. VTEK, (415) 335-1800.
Copyright 1997 Nelson Publishing Inc.
July 1997