Timo Liukkonen

Characterization of resolution cycle times of corrective actions in mobile terminals

Resolution cycle times for resolving issues raised by customers is one of the essential factors for indication of the customers satisfaction. The fact that there are many mobile terminals manufacturers implies that competition to grab and hold market share for a sustainable time is very strong. A forecasting model, based on a selected statistical distribution, is built up to give an estimation of the resolution time in three different category products. In this paper the model does not specify different failure symptoms reported by customers. Uncertainties and the reliability of the model buildup are discussed and example of an optimized correction action is given. Copyright

A case study of SPC in circuit board assembly: statistical mounting process control

A system was developed to continuously monitor the cycle times of successive placement machines in a long high-speed surface mount line. Statistical process control software was created to generate predefined out-of-control alarms when an unexpected change is monitored in the cycle times. The developed Statistical Mounting Process Control application was divided into three monitoring levels: line performance view, machine performance view, and pickup performance view (i.e, component feeders and nozzles). Most of the problems causing unexpected increase in placement cycle time are directly related to bad performing feeders or nozzles. The data transfer between the machines and host computer system is described. Out-of-control criterias selected for this statistical process control application are discussed in detail. One typical out-of-control situation is described for fast action and response to get the placement - process back to right track again. Promising results were observed after several weeks of evaluation of the system in two production lines: component pickup errors were decreased about 50%. In the future this is expected to have a direct positive impact on the output of the factory as well as on the total material cost and unexpected shortages, because component waste is simultaneously decreased. A theory is also discussed about poor pick-up performance having possible negative effect on the placement accuracy.

Six sigma analysis of SMD feeding parameters and board assembly quality

Purpose – Little interest has been shown in pickup conditions and parameters and their effect on placement accuracy in the literature before. The purpose of this paper is to find out the possible link between pickup conditions and placement accuracy of typical discrete chip components.Design/methodology/approach – A dedicated test board was developed and used to study the ultimate critical pickup conditions. Then the same board was used to find out the best parameters between ultimate conditions and perfect conditions in order to define working limits for good enough pickup that would work well in practice.Findings – The link between pickup conditions and placement quality was found and converted into measurable controllable values. Additionally, a problem was surprisingly detected in the placement machines vision performance resulting in inaccuracy, and parameters were re‐defined to avoid this problem in real‐world production. Based on all the findings, the best parameters were defined for component pic...

Decreasing variation in paste printing using statistical process control

Abstract A method was developed to evaluate the quality of the paste printing process. In this patented (USA) method a test pattern is situated on the printed wiring board, and the printing quality of the pattern is continuously monitored with automated camera based equipment right after the printing process. Statistical process control (SPC) application software generates predefined alarms when an unexpected change is monitored in the printing process. SPC rules used in the system are explained in detail. Promising results were observed after several months of evaluation: variation in paste printing process was decreased as well as the amount of defects in soldering inspection.

The effect of lead‐free solder paste on component placement accuracy and self‐alignment during reflow

The electronics industry will implement lead‐free soldering in the near future. Lead‐free implementation steps are divided into lead‐free process and lead‐free product. The eutectic Sn/Ag/Cu alloy seems to have become the most widely used alloy in the implementation of lead‐free processes. In this study, the requirements for component placement are discussed from the lead‐free process point of view. Experiments concerning the self‐alignment capability and tack strength of both tin‐lead and lead‐free solder pastes are presented. According to the results, a bigger variation in self‐alignment capabilities can be expected when using a lead‐free paste. The paste properties affecting the self‐alignment mechanism and tack strength are also discussed.

Increasing placement capacity with area based optimization and line balancing

Printed wiring board placement optimization of high‐speed placement machines in a high volume surface mount line was studied based on more careful analysis of the board layout beforehand. In this method, the target is to get the board area to be assembled as small as possible in each successive placement machine, paying the most attention on component coordinates already during preliminary line balancing phase. Optimization and line balancing principles, that had showed promising results already in the first studies when compared to globally used well‐known commercial optimization systems, were now further developed. Results presented and illustrated in this paper show remarkable, comparable, improvement in both cycle time reduction and in balance of the whole surface mount line. The main difference between this method and the advanced commercial solutions is explained in detail. Board layout, feeder arrangement, sequence of fiducial registration, and XY‐table movement were taken into deeper consideration in the method.

Available thermal budget in lead-free reflow process

The electronics industry will have to implement lead-free soldering in the near future. Lead-free technology implementation phases are divided into lead-free processes and leadfree product. The prime issue is the component availability and component heat tolerance with the higher soldering temperatures. There is concern about the stability and heat resistance of a range of plastic encapsulated devices, capacitors, filters, connectors and even printed circuit boards. In this study the process window size of the lead-free soldering process is compared for the current tin-lead process. Parameters affecting the soldering process, e.g. the temperature difference between a components top and bottom surface during the soldering, are discussed. Optimization of the reflow oven for lead-free technology is also discussed. Experiments are presented showing in some cases more variation in the normal reflow oven capability than what is the measured temperature difference between the top and bottom surfaces of the component, clearly highlighting the complexity of the problem in practice.