Sorting out defective products in SMT production is important. Even more important, however, is recognizing the interactions that ultimately lead to such rejects. The only way to achieve this is with hardware and software that constantly monitors and analyzes the production lines from start to end and make intelligent improvement suggestions for optimization.
DPMO – defects per million opportunities – is the key measure of quality assurance effectiveness. The overarching goal is to achieve a zero DPMO. To make this possible, quality-conscious electronics manufacturers rely on inspection systems that operate at high speeds without compromising their measurement accuracy. As a rule, the earlier you detect a problem, the less cost and effort it takes to fix it.
Fortunately, the solder paste printing process, which accounts for roughly 60 percent of production defects, is at the very beginning of the process chain. Although today’s paste printers have impressive capabilities – the DEK TQ platform, for example, features a machine accuracy of ±12.5 microns @ 2 Cmk and a wet-print accuracy of ±17.0 microns @ 2 Cpk – many other factors such as the stencil design and material, the solder paste type or the cleaning cycles have major impacts on the final result. The increase in miniaturization also leads to ever finer solder paste deposits, whose interspacing is also getting smaller and smaller, especially in fine-pitch applications – to as little as 50 microns. This places significantly higher demands on the printing process and increases the probability of defects. In volume production, disruptive factors can quickly increase exponentially, frequently resulting in circuit boards that do not meet the high-quality requirements.
Consequently, this is precisely where modern solder paste inspection systems come into play. The Process Lens from ASMPT, for example, measures each solder paste deposit and detects even the smallest deviations and trends. A DLP chip with up to 20 million individually controllable micro-mirrors checks each deposit for volume, height, area, shape, and position. The system first detects relevant areas on the PCB via a 2D scan and then measures them in 3D with a resolution of up to 10 microns: resulting in up to 80 percent fewer false calls compared to conventional SPIs – all while operating up to 70 percent faster than conventional devices.
This performance reserve makes it possible to execute additional measurements that do not lead to an increase in overall production time, such as foreign object detection or the mixed mode of the Process Lens HD platform in which both solder paste deposits and glue dots are examined. The Process Lens HD is also one of the few SPI systems on the market whose measurement resolution can be controlled via software. With its future-oriented features, the Process Lens HD system is ideally equipped for the product generations of the next few years, making it a worthwhile investment.
With an SPI system, manufacturers can detect many manufacturing defects at an early stage and remove the affected boards from the production flow. In the subsequent placement and reflow processes, however, further problems can occur, such as offset or missing components or the dreaded tombstoning. Anyone who manufactures with particularly high-quality standards, for example for the automotive industry, therefore needs additional Automated Optical Inspection (AOI) systems at the end of the line, with preferably another before the oven. These systems reliably detect defects on each circuit board and prevent unusable products from being delivered to the customer.
Although these systems can prevent customer complaints or contractual penalties, they often do not get to the root of the problem because the associated software usually considers only the individual product – i.e., the individual defect – but not the interactions that led to its occurrence. Experienced specialists then must search for root causes and laboriously combine data from the machines on the line by hand. As a result, it is not uncommon for sporadically occurring errors to remain undetected.
Innovation and market leader ASMPT is embarking in a new direction with its WORKS Optimization quality assurance system. Using the standardized IPC-2591-CFX interface, the intelligent application from the WORKS Software Suite includes all machines on the line in its defect analysis as it integrates and visualizes the data. In combination with the Process Lens from ASMPT or a third-party SPI system, the printing process can run completely autonomously without any operator assists. The system can also trigger an automated offset correction, a cleaning cycle when needed or print parameter optimization.
If SIPLACE pick-and-place machines are in use, WORKS Optimization focuses the operator’s attention to the sources of the largest process deviations and prioritizes the proposed solutions in order to maximize the efficiency of the operator action. Cross-product and multi-line analysis and intelligent data visualizations pinpoint defect root causes quickly and identify problems that might otherwise go undetected.
In developing this solution, ASMPT benefited from its many years of experience. The technology leader covers almost the entire SMT manufacturing process with its product portfolio and has been able to build up deep and comprehensive process know-how over the years. This wealth of knowledge was fully incorporated into the development of WORKS Optimization.
The analyses and dashboards have been designed to allow even new employees to quickly perform their respective jobs. And since WORKS Optimization is compatible with the WORKS Operations application from ASMPT, messages from WORKS Optimization can be forwarded as tasks to a remote workstation or to the mobile device of an operator who is a qualified member of a pool of experts. Also practical and time-saving: After they have been detected, defects are displayed not only on the central console but also on the display of the affected machine and can thus be handled immediately by the operating staff.
WORKS Optimization consists of three modules:
In accordance with ASMPT’s modular, flexible and manufacturer-independent automation concept, WORKS Optimization also permits the integration of third-party SPI and AOI systems via the standardized IPC-2591-CFX interface.
For the user, the Process Lens system and WORKS Optimization deliver a series of benefits as improvements extend across the entire production line. This results in more stable, defect-free processes, better quality, shorter NPI times, less scrap, and significantly lower costs overall. WORKS Optimization is an intelligent and integrated expert system that sets new standards, particularly with regard to its practice-oriented functionality. It relieves scarce specialists from routine tasks and allows them to focus on achieving maximum productivity. A DPMO value of zero is thus within reach.
