Solutions for a better world

11 years later, in 2019 part of the manufacturing plant was in need of an upgrade to the latest standards, and again, Ersa was chosen as the system supplier for both processes. A VERSAPRINT 2 Pro² and a HOTFLOW 4/14 were installed. The VERSAPRINT 2 Pro² is successor to the successful VERSAPRINT S1-2D. Just like its predecessor, it has integrated 2D inspection for a 100% check following the printing process. Why only 2D? An intelligent testing strategy is able to detect faults in good time.

The crucial aspect is to know what form this strategy must take during product development. In other words, at which points in the process chain does assembly testing make sense? There is a wide range of testing possibilities available including SPI, AOI, AXI or in-circuit-testing. It must be examined which of these tests makes the most economic sense and is most target-oriented. Whichever is used, it must always be matched to the respective product-specific requirement.

How much inspection effort is required after stencil printing in order to guarantee reliable assurance of manufacturing quality in the SMT process? Does it have to be 3D inspection, or is two-dimensional inspection enough? The fact is that stencil printing is still the one process step in the SMT line with the highest fault potential – at almost 70%, a 100% inspection should be a must on every manufacturing line.

Over the past few years, the inspection options and methods have changed. For years, the partial 2D inspection integrated in the stencil printer was the only inspection after the printing process. This was sufficient for a long time if only one or two integrated circuits (IC) were on the assembly for example. As assemblies became more complex and components became smaller, the time came for external 2D inspection systems that made 100% inspection possible. Driven by even smaller components and more complex assemblies, the development and introduction of 3D inspection was bound to follow, and consistent with development. Yet this is where the problem starts for many users: which process limits are correct, which limit values have to be set? 3D inspection requires a lot more effort and even the IPC does not provide recommendations for process limits. The high component mix, the stencil ratios related to thickness and opening selected often in a mix with steps, the solder paste used and the quality of the printed circuit board are the main deciding factors for the final product: the solder joint as the connection between component and printed circuit board.

Another important factor that plays a role in the selection of test systems is cost – not just the investment involved but operating costs as well. Special maintenance and service as well as qualified personnel are necessary to make the most of the possibilities provided. It does not make much sense to purchase a highly technical, high-resolution inspection system and then only use a few basic functions and set default values. All manufacturers must decide which tools and quality tests are required to achieve the optimum first pass yield with their manufacturing line.

Back to the solder paste print: depending on the component spectrum, 2D inspection can detect almost the same number of faults as 3D inspection. It is favourably priced and simple in the definition of process limits. The IPC provides recommendations for this: 70% cover with a reduction of the opening by 10% compared with the pad surface. The expectation is clear – zero faults in the ideal case. This takes us back to the beginning – process development. Here, manufacturing lines with only their own products are clearly one step ahead. The non-observance of layout rules and the infringement of design rules are always exposed and make a continual improvement process for product development possible. This puts companies like TELE Haase at an immense advantage on account of their structure. Everyone feels part of a community, and people work with rather than against one another.

The software platform of the VERSAPRINT 2 Pro² including setup is even clearer and more intuitive than with the VERSAPRINT S1-2D. The HMI is primarily designed as a touchscreen, and guarantees faster understanding and greater acceptance by operators, particularly during the programming and setup of new and existing programs. The monitor setup in portrait format increases accessibility to the machine and creates space in the manufacturing environment. The monitor can be adjusted to operator height by simple tilting, and support setup in the printer by being pivoted towards the operator. Or it can be pivoted completely away to the side to create more space in front of the machine. This has been very well received in the manufacturing environment. It goes without saying that the VERSAPRINT 2 can be integrated in line management systems such as HERMES in accordance with IPC-9852 or IPC-CFX as a universal gateway for connection to MES solutions.

A further feature of the VERSAPRINT 2 Pro² is the integrated dispenser function. This option makes it possible to dispense adhesive and/or solder paste on the printed circuit board after the printing process. As circuits become miniaturised, the template thicknesses used are shrinking, between 100 to 120 µm. This means that with typical mixed placement, some components cannot be provided with sufficient solder volume. The solution can be the use of stepped stencils, even if more solder is often only required in a few spots. Or a dispenser is used, providing a simple way of dispensing the required additional solder. These systems are used even more often for dispensing adhesive. During the reflow process in particular, if heavy components such as coils are mounted on the first side, they are fixed with adhesive to prevent them from falling off during the reflow process.

The dispenser used makes use of the Archimedes’ screw system, thus creating the precondition for positioning points extremely precisely. The dispensing programs can be prepared easily, since the entire layout of the printed circuit board can be seen on the monitor – just as for all the other processes. Simple zooming to the required position plus marking represents maximum user friendliness. Parameters can be set individually for each point, and inspection is, of course, possible after the dispensing process.

Gerhard Sattler explains the decision in favour of 2D inspection rather than the popular 3D inspection method: “The decision was easy thanks to our experience with VERSAPRINT S1-2D and our fault rate at the end of the line. A 3D SPI would not have significantly improved the fault detection rate. And for us, 2D inspection is a favourably priced way to optimise our manufacturing process compared to 3D. In addition, both systems, the existing S1-2D and the new VERSAPRINT 2 Pro², offer the option of upgrading to 3D inspection. This means we will certainly be in a position to face future challenges.”

Another important aspect in favour of the Ersa systems is that the type of manufacturing at TELE – batch sizes between 2 and 1,000 have to be managed, and fast setup and retooling are absolutely necessary. Both systems provide optimum preconditions for fast setup changeovers in this case. Both the software and the accessibility of both systems make setup irrelevant. “The decision in favour of the Ersa systems was the right choice for our manufacturing line,” Sattler concludes.