Optical inspection made to measure
An effective inspection solution for small batches from a batch size of 1
The optical inspection of small production batches calls for approaches beyond AOI. Augmented reality inspection combined with inspection by part number has become established as an effective method. To automate the handling involved in capturing the images, proServ electronic from Witten has implemented an intelligent inline solution.
published in Productronic 11/2017
Small production batches present EMS providers with very similar challenges to medium and large series. The work in the run-up to production is almost identical. A considerable amount of time goes into preparing the data, preparing production and programming and setting up the production machines. Relative to a single board, the time invested per PCB produced is much greater for small batches than for large series.
The economics
Looking at the optical inspection of small batches under these conditions, the ratio is considerably worse. Although the purpose of AOI is to automate optical inspection, it cannot fulfil this task for first-time small batches. All the PCBs in the small batch are often needed to parameterise the AOI program correctly. Throughout this time, a well-trained AOI operator is required to resolve the unavoidable false calls and incorporate them as program improvements. With this approach, none of the boards is really inspected “automatically”. In addition to the high staff and time requirements during inspection, creating the program itself is also time-consuming (cf. Figure 4). If the total effort is converted to a single PCB, the cost of automatic inspection per board in a small batch is very high. Customers are often unwilling to bear these costs.
As an alternative to AOI, inspection is often purely manual. This method offers little reliability. The inspection process cannot be traced. There is no documentation of the complete inspection. Inspection staff are expected to concentrate intensely, which, however, also leads to rapid fatigue. Information needed to assess the PCBs has to be looked up in the documentation. Naturally, this method also offers too little certainty for the customers.
EMS provider proServ electronic
In 2016, proServ electronic from Witten was looking for a suitable system for the optical inspection of small batches. The existing AOI could not meet the requirements. The aim was to find a method for the optical inspection of small batches that is quick and easy and, as an alternative to AOI, offers a degree of automation in the process and in supporting the operator.
proServ electronic was founded in 1999 and has grown considerably since then in line with its customers' consistently high requirements and needs. Its most recent move to larger premises took place in 2015 and now provides 1,500 m² of modern production space. Continuous investment in machinery ensures great flexibility in meeting all customer requirements, so that series of any size can be produced without difficulty. One line is reserved exclusively for producing prototypes, pilot runs and small batches. The qualified staff work with a strong sense of quality.
proServ electronic found that the EFA Inspection system from Lebert Software Engineering in Hanau met its requirements for the optical inspection of small batches.
An efficient inspection system for small batches
In EFA Inspection, programming is quick and easy, without any great loss of time. On average, programming takes 5 minutes. All relevant data, such as the pick-and-place list, the BoM data and the assembly plan, as well as production notes or additional information for each component, can be integrated. All this information is available in a targeted way during inspection. The augmented reality functionality overlays the information on the image of the board at the component currently relevant.
To cover different inspection tasks, a wide range of inspection sequences and display modes is available. For example, inspection by part number displays and assesses all components with the same part number together (see Figure 3). The image sections of the components are rotated back to zero degrees according to the stored rotation angle. For the inspector, this means that all components of a part number must look the same.
“The flexibility with which we can adapt EFA Inspection to our process is an important factor for us,” explains Managing Director Sabrina Frühinsfeld.
Inspection using the golden board function is also possible. Here, the images of a good board and of the board under test are displayed alternately. The two images are aligned via fiducials, which makes the alignment extremely stable. The inspection sections can be set up individually and thus adapted to the characteristics of each board.
For small batch inspection, the inspection procedure can be fixed so that the operator no longer has to set anything up. The next image captured is loaded automatically and displayed for inspection. The process is thus guided, repeatable and documented. In addition, the augmented reality display supports employees in their inspection decisions. All relevant information for the assessment is available at a glance. The average inspection time for a PCB with around 500 components is 3 minutes.
For a batch size of 20 boards, this means a total effort of about 65 minutes including programming. By comparison, the set-up time of the AOI alone for the sample board is already about 120 minutes – not counting the false calls. (see also Figure 4)
Inline functionality without handling effort
The system is based on a high-resolution image of the board. With the EFA desktop unit, capturing the images involves a certain amount of handling for inserting and imaging the boards. When EFA Inspection is in continuous use, this handling effort is certainly significant.
An EFA inline unit is available as an alternative (see Figure 5). Combined with a loader and unloader, it captures the images automatically. A magazine of boards to be inspected is placed in the inline unit and the corresponding imaging profile is then selected. The conveyor width is set automatically from the profile and the automatic imaging process for the magazine starts. Once the images have been captured, the boards are sorted back into the magazine. This inspection island with inline functionality is available for many applications. Images of THT-assembled boards are, of course, also possible.
The complete images are transferred to inspection stations, where inspection can even take place in parallel. The images are loaded automatically into an open EFA project, so that the operator only has to concentrate on assessing the image sections displayed.
“The EFA inline solution won us over with its automatic image capture,” reports Marco Schönefeld, Managing Director of proServ electronic. “This lets us inspect batch sizes from 0 to 1,000 with EFA Inspection without any problems.”
A smart solution for work preparation too
However, proServ electronic also decided in favour of EFA SmartSuite because of the system's flexibility and expandability. Besides inspection, EFA is also of interest for work preparation. Data preparation for the machines is now also done with EFA SmartSuite. The different formats of the customer data are imported into EFA, and the data for the company's own production is always output in the same format. This saves a considerable amount of time, because uncertainties and repeated data preparation in production are now a thing of the past. “With EFA, we can convert the various formats of customer data into a standard format for production,” reports Marco Schönefeld.
As a result, EFA Inspection, the EFA inline unit and the use of EFA SmartSuite have achieved significant time savings.
“This has a direct effect on the quality of our products,” explains Managing Director Sabrina Frühinsfeld.
proServ electronic is planning further integration of EFA SmartSuite. The next step is to connect it to the ERP system. The fuzzy search algorithms will then find the right part numbers directly from the imported customer BoM. EFA SmartSuite interprets the individual values, so that notation, units or the order in which the component description is listed play no role.
EFA SmartSuite is designed as a complete solution for EMS providers (see Figure 6). The various EFA applications can be used from the quotation phase through work preparation to production, and their smart automatic functions optimise production steps that were previously purely manual.
“In the continuous further development of EFA SmartSuite, we rely on close cooperation with our users,” explains Hans Jörg Lebert, Managing Director of Lebert Software Engineering.
This ensures that every customer can find their individual solutions in personalised workflows – the result is a practical application “by customers for customers”.