The screwdriving process in the production of electrical components is a crucial step that requires precise planning and careful consideration. In this technical article, the decisive factors for efficient screwdriving are discussed, starting with the selection of suitable screwdriving partners and screws, the correct handling of the screws as well as the requirements for cleanliness and the right screwdriver.

Choosing the right fastening partner

The selection of fastening partners is of fundamental importance, as they form the basis for a successful fastening. The type of material being screwed into plays a decisive role. Whether it is plastic or metal such as copper, aluminium or steel influences the choice of screws. Particular care must be taken with sensitive components such as printed circuit boards (PCBs), as they can only be subjected to limited loads, and the precise alignment of the screw partners is of great importance. Special hold-down devices or screw masks ensure exact positioning, whereby it is also possible to press the component together accordingly.The condition of the component, in particular the presence of interfering contours such as steps or other components, must be carefully checked. Equally important is the accessibility of the screwing points for the screwing unit. The screwing direction can be vertical from above or below, horizontal or at an angle. The number of screws and their position, including possible height differences, must also be taken into account.

Determining the right screws

The screwdriver must fulfil certain requirements. Different screw types play a role here with regard to the head type and head diameter as well as the appropriate drive type. Feeding the screws by feed requires special planning. The ratio between the head diameter and the shank length is very important to ensure smooth feeding. An incorrect ratio can lead to the screws twisting in the hose and being fed in the wrong direction. In such cases, solutions such as T-shaped profile hoses or the pick-and-place method are ideal.

Compliance with cleanliness requirements

Strict cleanliness standards are essential in electronics production. To prevent contamination, dirt locks can be installed at various points, such as after the feeder or before the mouthpiece. The cleanliness of the system also depends largely on the condition of the supplied screws. Ideally, the screws should be cleaned and then vacuum-packed; to prevent contamination, it is necessary to mask or cover screw points appropriately. The screws are often not fed directly over the component, but over the mask or outside the component. Optionally, extraction and/or cleaning directly at the screwdriving point can also be considered. To ensure cleanliness, the nosepiece or bit is cleaned using a special cleaning box with vacuum.

Selecting the right screwdriver

The selection of the right screwdriver depends on several factors. The decisive factor is the automation class, which determines whether an automatic or manual screwdriver is used. In addition, the screwdriving case classes according to the applicable general standards play a central role. These classes, namely class A for safety-critical applications, class B for function-critical applications and class C for customer-critical applications, define the requirements for the screwdriver.
The screwdriving classes determine the equipment of the screwdriver. For example, class A requires a redundant torque measurement system, either through two sensors or through redundancy via the current consumption, and depending on the selected screwdriving method -be it gradient, torque, angle of rotation, depth or yield strength -the screws are tightened using various parameters. Important parameters such as torque and angle of rotation are continuously monitored. The screwdrivers have different control variables and types that offer more or fewer functions and provide data on the screwdriving process. There are various interface options such as Profinet,
Optimising the screwdriving process in electronics production
provide data on the screwdriving process. There are various interface options such as Profinet, Profibus and MES connection and, if necessary, a vacuum screwdriver can be used. The screw is sucked into or fixed in the nosepiece, which is particularly important for screwdriving points that are difficult to access.

The screwdriving process in detail

The actual screwdriving process requires careful planning. This planning is based on a variety of customer requirements and varying screwdriving standards, which means that the sequence can vary considerably. A typical sequence might be slow tightening of the bolt, followed by faster tightening to a specified torque or angle, and finally final tightening to the specified torque or angle.The order in which the bolts are tightened is important and can vary depending on the specific requirements. For example, it may be necessary to use diagonally opposed screws or a specific pattern, and appropriate measures must be taken in the event of an improper (NOK) screw connection. This may include repeating the fastening or ejecting the component for rework. A major advantage of the bolting process compared to welding or gluing processes is that joints can be loosened.

Optimising the screwdriving process requires a comprehensive consideration of all relevant factors. This begins with the selection of suitable screwdriving partners and screws, extends to the appropriate screwdriving technology and control and has a decisive influence on the cycle time to be achieved. An efficient and clean screwdriving process is crucial to ensure the quality and reliability of assemblies in the production of electrical components.