Press Release

How well can you “Pin Down” defects in press-fit assembly?

2018-11-14

Abstract

The automotive safety system has gained increasing attention in the electronics manufacturing sector, owing to a rapid electrification of vehicles. The manufacturers are introducing new safety electronics safety systems and solutions, which need to be high quality, reliable, and environmentally friendly. Therefore, maintaining a balance between cost and quality is always a challenge for every manufacturer in this market.

What are some ways to resolve these issues while improving profit margins? The answer lies in efficiency improvements to the overall backend process. During this final stage, manufacturers add high-value components and packages to the assembly. This is where the press-fit operation truly shines. Press-fit technology is a lead-free solderless electrical assembly process, where mechanically compliant pins are inserted into a printed circuit board (PCB) plated through hole (PTH). Although this technology offers many advantages over soldering, it is challenging to ensure minimal defects due to board complexity. As a single defect in the automotive industry can result in fatal vehicle accidents and hundreds of thousands of recalls, it is crucial to “pin down” defects early in the stage. Equipment suppliers like Koh Young Technology are working diligently to expedite the adoption and implementation of precise pin inspection.


Press-fit vs. Soldering

The soldering process has been used in the industry for years because it provides a cost-effective, reliable process to connect electrical wiring and components onto a PCB. However, the shift towards lead-free soldering placed a substantial economic burden on manufacturers as they moved to use more expensive plastics like liquid crystal polymer (LCP), p-phenylene sulfide (PPS), and polyphthalamide (PPA) to cope with higher soldering temperature.


On the other hand, press-fit technology does not use solder alloy, instead it uses compliant pins with a slightly larger diameter than the PTH. This press-fit process eliminates common soldering problems like cold joints, solder bridging, and more - press fit technology offers high reliability. As shown in figure 1, the press-fit connection has a failure rate of 0.005, which is at least ten times more reliable than soldering. As such, the pin-insertion machine market is at a CAGR of 4.9 percent between 2016 and 2022 and reach 276.7 million USD by 2022.

Type of connection

Details

Conductor cross section (mm)

Failure rate

λref in FIT

Notes: Standards/Guide

Solder

Manual

Machine

0.5

0.03

IPC 610, class 2

Press-fit

0.3-2

0.005

IEC 60352-5

Wire Bond

Al

Au

0.1

0.1

28μm / Wetch bond

25μm / Ball bond

Wire-wrap

0.05-0.5

0.002

DIN EN 60352-1/IEC 60352-1

Crimp

Manual

Machine

0.05-300

0.25

DIN EN 60352-2/IEC 60352-2

Termi-point®

0.1-0.5

0.02

DIN 41611-4

Insulation Displacement

0.05-1

0.25

IEC 60352-3

IEC 60352-4

Screw

0.5-16

0.5

DIN EN 60999-1

Clamp

Elastic force

0.5-16

0.5

DIN EN 60999-1

Figure 1. Table showing reliability of different electronic assemblies according to the IEC 1709


Need for Accurate Inspection

Pin connections for electronics modules often occur near the end of the final assembly process. Yet, if manufacturers find defects at this stage, the PCB must undergo arduous rework or, in some cases, scrapped altogether. Therefore, manufacturers must accurately inspect the boards beforehand. Various testing methods are available such as manual inspection, electrical test, x-ray inspection, and more. However, some techniques are becoming obsolete as board complexity continues to increase. In fact, some boards can have over 100,000 connector pins on them.

Even worse, these pins are getting shorter and smaller. Traditional methods can no longer detect crushed and bent pins. Automated optical inspection (AOI) is a visual inspection process for the entire PCB. The camera autonomously scans the board and can detect most of the backplane faults including critical defects (e.g., missing pins) and quality concerns (e.g., deviated pins, bent pins). The AOI system would be the optimal choice to achieve the quality requirements of assembly.


Pin Inspection with 3D AOI Capability

Realizing the growing importance for accurate inspection, Koh Young has developed the KY-P3 pin inspection dedicated solution. It designed the KY-P3 3D pin inspector to identify common defects like missing or potential pin offsets, as well as to identify co-planarity by accurately measuring the pin-to-pin distance. (Figure 2) Like its other AOI systems, the KY-P3 uses a Koh Young patented shadow-free Moiré technology to measure the z-axis profilometry of the entire board. Koh Young uses the height threshold to extract the pin body and pin tip information. This dataset allows the KY-P3 to provide a reliable pin height and offset measurement with CAD dimensions because it accurately locates the pin body during the very first stage of the inspection process.

Figure 2.3D single pin & conventional press-fit measurement using the Koh Young KY-P3 system




Superior Flexibility Combined with Proven Accuracy

Among many inspection items, the strength of KY-P3 lies in its height measurement, which guarantees 0.75 percent accuracy for any pin types up to 25mm height. (Figure 3) When it comes to measuring height on a pin with an angled or pointed tip, the challenge is complicated compared to pins with the more common flat tip. The KY-P3 uses a height range algorithm that sets a minimum and maximum height to calculate the average height. Using a relatively high height range, manufacturers can obtain accurate height information for sharp pin tips.


Figure 3.Chart showing the KY-P3’s measured calibration target results


Accurately extracting the pin tip translates to an accurate pin offset measurement. Manufacturers use a specific vertical distance below the pin tip to locate a suitable measurement plane that reflects the full pin. Then, the calculated center point of the measurement plane is used as a reference point to measure the absolute and relative pin-to-pin distances. (Figure 4) Ultimately, the KY-P3 helps manufacturers ensure maximum alignment accuracy, which is essential in producing high-quality PCBs.

Figure 4. Pin offset measurement using the KY-P3 system



Increased Efficiency, Reduced Costs

There is always a drive to improve profitability. The synergy between the KY-P3 system and the Koh Young KSMART software allows manufacturers to improve the overall process. Manufacturers can monitor the pin-insertion machine performance in real-time using RTM@KSMART. The software module allows manufacturers to monitor and manage Cpk data by part, job, or fixture in real time. Going further, SPC@KSMART instantly visualizes analyzed data with relevant indicators like yield rate, NG analysis, PPM analysis, Gage R&R, offset analysis, and more. The KY-P3 can generate a significant set of reliable measurement data to help manufacturers optimize the pin-insertion machine fixture and adjust tolerances to meet customer’s specifications on Cpk (e.g., Cpk 2.0 levels.) Combining KSMART and the KY-P3 can help manufacturers accelerate productivity improvements, reduce the ROI, and realize a Smart Factory.


Conclusion

The press-fit operation is becoming much more prevalent in the market, thanks in part to its many advantages over traditional soldering methods. However, it is becoming more challenging to inspect press-fit pin defects, because the pin dimensions are shrinking and the placement density is increasing. The industry needs a high-precision inspection solution to overcome these challenges. Koh Young, the leading 3D measurement-based inspection and solutions provider, brings new levels of repeatability and accuracy for press-fit operations with the KY-P3. Ultimately, the KY-P3 would not only “pin down” defects in the press-fit operation, but it will also improve the entire manufacturing process.

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