Complete Versatility with High-Throughput X-ray

While they are essential characteristics of an AOI system, 3D inspection and high speed are just as important for AXI. With time-optimized image acquisition technologies and efficient handling concepts, in-line X-ray performance is continually 

In the inspection of electronic assemblies, especially for components with hidden solder joints such as ball grid arrays (BGA) or quad-flat no-leads packages (QFN), automatic optical inspection (AOI) is insufficient. Random samples with MXI arise as one option, but this is not always the optimum solution. Where product safety plays an especially crucial role, particularly in the automotive area, a fast, thorough inspection of solder joints is needed. This calls for a fully automatic in-line X-ray inspection (AXI), which also satisfies the speed constraints. On such a system, throughput is heavily determined by the inspected assembly handling, since a fully protected housing with mechanical gates is necessary.

Fast, precise changeOne ingenious solution to the in- and outfeed of the assemblies can reduce the time to change them to under four seconds. This results from a hardware concept that works with several printed circuit boards that can be in the system simultaneously and are moved in overlapping time slices. Because of the shortened paths, the corresponding switching of assemblies from one position to the next is extremely quick and precise. This reduction in handling time reduces the idle time necessary as overhead just to change assemblies. The actual productive time is the pure analysis time, in which the images are captured and evaluated. Thus, if the handling is reduced, e.g., from the previously typical 10-12 seconds to 4 seconds, with a pure analysis time of an additional 10 seconds, total throughput time is 14 seconds instead of 20 seconds – a gain of 30 percent. Even with just this aspect in mind, a comparison of the available systems is definitely worthwhile. Optimizing the analysis time can bring additional significant throughput gains. During program creation, the time-consuming 3D inspection can be restricted to those components for which it is truly necessary. Everywhere else, faster orthogonal and angled processes are employed.

First-class 3D AXI hardwareOptimized solutions for fast image acquisition also have a positive effect on the analysis time. High-value linear motors, which ensure that flat panel detectors on a cross table (xy-table) can be moved quickly to the different positions, sharply cut image acquisition times for variably angled radiation penetration, especially when acquiring several views for 3D reconstruction. With the right settings, electronic assemblies can also be optimally represented in the 3D image from predefined perspectives. Experience points out, e.g., that for structures generally arranged on a grid, such as BGA balls, irregularly arranged acquisition positions are recommended. Because of the resulting suppression of periodic structures, artifacts can be largely eliminated, significantly improving the 3D results of the planar computed tomography (PCT).

During the development and revision of an AXI system, particularly in this context it has proven expedient to lay out the overall 3D inspection area with ample space, to give the ultimate user complete flexibility in selecting the acquisition angle. In addition to larger penetration angles and different perspectives, leading to better 3D results, larger printed circuit boards can be inspected. For high throughput, the use of a flat panel detector with as large a field of view as possible is important.

Many useful optionsThe 3D reconstruction processes are central in determining the quality of the 3D reproduction of the acquired scene. Besides simple and fast methods such as the addition process, the Viscom AXIs implement the FDK process (Feldkamp, Davis, Kress). Dirk Nülle, managing AXI product developer at Viscom and responsible for the new X7056-II 3D AXI system: “This special process of filtered rear projection delivers better slice image reconstructions, especially for BGAs. However, it does take somewhat more computation time.” For a user-friendly display on the one hand, but for basic image improvement too, there are also appropriate aids such as contrast filters or the possibility of grayscale value adaptation (gamma correction). So that all results are flawless, even for sagging printed circuit boards, it is also possible to add a height correction to the automatic inspection run. This is accomplished by a tool that correspondingly adapts the individual inspection positions. The calculated sag model of the electronic assembly is then applied for each inspection method.

The inspection system software should be as easy to operate as possible. One example: The user can specify 3D AXI acquisition positions, has various resolution stages to choose from thereby, and decides on a number of viewing positions appropriate to the application and desired inspection depth. Later, depending on the task, a selection between these predefined 3D cameras can be made. Again depending on the task, either inspection quality or cycle time is the priority. “In our experience, at least nine views are necessary to realize 3D. Yet sometimes, it turns out more acquisitions are needed, depending on shadowing and on which components are in opposite positions on a printed circuit board assembled on both sides,” states Dirk Nülle.

Balanced combined solutionAdditional advantages arise when AXI and AOI are integrated in a single system. With this combination, not only can the proportions of orthogonal, angled and 3D X-ray be optimally tuned to each other, but by inclusion of the optical inspection methods their use can be reduced to a minimum, which in turn further improves the cycle time of the entire inspection while – as an often overlooked effect – the radiation load on individual components is lowered. Some criteria, most apparently the example of OCR (optical character recognition) – recognizing plain text on the component – must be conducted purely optically; in other cases features can be captured either optically or with X-ray. Logically, other effects can only be inspected with X-ray technology methods.

The operating convenience of such a combination system can extend to integrated automatic inspection program creation and the use of an inspection simulator with which the user can run through different inspection scenarios off-line, e.g., with greater weighting of the inspection quality, the costs or the speed.

Wide offering for X-ray applicationViscom offers complete versatility for X-ray inspection of electronic assemblies. The X8011-II PCB is extremely successful in the MXI area. For heavy components up to 15 kg and a sample size of up to 722 mm diameter, the otherwise similarly technically equipped system X8068 is ideally suited. For in-line X-ray inspection, the X7056RS has been used around the world for many years. When purchasing, a majority of the users decide to integrate an appropriate optical inspection solution from Viscom. The new version of this popular system is the X7056-II – equipped with the innovative handling concept xFastFlow, which can in- and outfeed printed circuit boards in less than four seconds, and also designed as a combination option with 3D AXI and 3D AOI. The X7056 series offers the possibility to order the so-called “AOI-prepared” version, so the customer can deploy an AXI system that can later be quickly and economically extended with the AOI option. The X7056-II is available with the Viscom software vVision to offer the same ease of operation the company has already realized for its AOI as well as SPI and CCI systems; that is, also for solder paste and conformal coating inspection on electronic assemblies.

For more information, contact Olaf Szarlan, marketing, at Viscom AG at Carl-Buderus-Straße 9-15 – 30455 Hannover; +49 511 94996-718; Email:; Web site: