Applying Lean Principles to Line Design Print E-mail

A holistic way to evaluate equipment selection and process improvement.

EPIC Technologies has long taken a holistic approach to Lean manufacturing that focused on maximizing throughput and flexibility by minimizing variation in production flow. From an equipment selection standpoint, desirable characteristics include high throughput, minimal changeover time and broad process windows.

EPIC has standardized equipment selection throughout all facilities to make it easier to transfer process improvements and/or projects among facilities, plus reduce the added workload that wide variation in equipment and processes can generate. Consequently, when we decided to upgrade our standard placement equipment to better support a shift in its customers’ requirements to small package sizes, the evaluation process involved more than simply adding a line. 

The new standard configuration includes a DEK Horizon 02i screen printer, a Koh Young KY8030-2 3D inline solder paste inspection system, three ASM SX-2 placement machines, a Vitronics Soltec XPM3i reflow oven and an Orpro Vision Vantage-S22 automated optical inspection system.

From a throughput standpoint, line design strategy focused on automating processes closely tied to product quality and balancing placement speeds with the reflow process.

Automating inspection at two critical points in the line both improved quality and eliminated labor. The SPI adjusts screen-printer parameters whenever they appear to drift outside of control limits. Similarly, the AOI automatically shifts printed circuit board (PCB) assemblies failing test to a reject buffer and provides trends data that can help an operator quickly correct any systemic issues. In both cases, time an operator would have spent in manual inspection processes has been eliminated.
The operator is now focused on addressing any corrective actions needed after AOI identifies a potential issue.

Throughput goals were achieved by integrating a reflow oven with 12 heating zones and four cooling zones. This offered both the best range of flexibility for different PCB types, plus maximum throughput. The oven’s software is integrated with a KIC profiler to support rapid development of accurate profiles with minimal engineering time.

The placement equipment can support package sizes as small as 01005 and package-on-package (PoP). From a volume standpoint, it is capable of 1.3 million placements per day. From a Lean perspective, it drove other efficiencies as well. EPIC’s production environment is high mix and variable demand. That drives strong emphasis on single minute exchange of die (SMED) philosophy. The heads on the placement machines can be changed over in fewer than 10 min., and the gantries can be changed in 30 min. Previously, those operations took several hours. Routine preventative maintenance on the line averages less than 1 hr. per week, and more extensive maintenance tasks have been pushed to quarterly and six-month intervals.

The new configuration ties in well with the company’s Lean Sigma improvement initiatives. Miniaturization and higher PCB complexity increases the opportunities for defects, particularly with BGAs. Prior to equipment acquisition, a kaizen event held to evaluate the top contributors to scrap found BGAs and ICs showing spikes. Automated monitoring of solder paste height and inline AOI were identified as tools to address this issue. The Lean Sigma team is now utilizing data from these tools to evaluate optimum choices in solder paste, stencil patterns and reflow profiles for higher-complexity product.

As an example, one recent study utilized the inline AOI defect report to identify that the major defect type in the product group under analysis was tombstoning. The AOI report provided a graphic image of the PCB showing where the defects were occurring. Red markers highlighted the components failing in the selected time interval. The size of marker indicated how many times a specific component failed relative to the number of tested panels. A cause-and-effect diagram was created, and it indicated that the two variables most likely causing the defects were solder paste misalignment and volume differences between terminals.

The team then analyzed the raw data from the SPI and compared volume differences between terminals. It was determined that there was not a significant volume difference, so this was not the root cause of the tombstoning issues.

After screen printing, SPI was used to study the PCB more closely. It was determined that the solder paste was shifted in the Y axis, and results showed that deposits had an offset of up to 3 mils. This was significant enough to cause tombstoning. While bare PCBs did not show this misalignment, further analysis showed that the PCB was stretched after the first reflow pass. The stencil was redesigned to reflect the dimensions of the PCB after reflow, which eliminated the tombstoning issue.

Production equipment hasn’t changed dramatically in terms of the operations that are performed. However, factory automation software and the ability to seamlessly integrate equipment are continuing to improve. These improvements, combined with a robust Lean Sigma strategy, help ensure superior quality in high-complexity PCB production.

Edward Basconi is director of engineering at EPIC Technologies (; This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Victor Contreras is test and manufacturing engineering manager at EPIC; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .



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