Application of press-fit technology in automotive electronics
2021-04-25
- From June 2016 [ Smart Car Journal ] " Change The World " section
Learn more about the technology trends and reference designs of the Smart Car Journal .
Market demand has been extremely high for economical car navigation, infotainment systems, electric and hybrid powertrain systems. A variety of advanced vehicle safety features, such as anti-lock braking, stability control, and sensor-controlled tire pressure monitoring, are booming. Automakers need cost-effective strategies to design and assemble highly durable electrical and electronic systems.
Manufacturers are gradually turning to press-fit technology to strengthen and replace weld locations. In the press fit technique, the spring pin and plated through hole (PTH) are the main components. The PTH is drilled into a layered circuit board and is plated using copper plating to form an electrical circuit on the inserted portion of the press-fit pin. The main advantage is that the connections and electrical contacts are highly reliable.
Standard press fits used in other industries can also play a good role in controlled environment applications. Automotive applications require higher current carrying capacity and better resistance to vibration, thermal shock and various environmental conditions. Technological advances can address these challenges by convincing OEMs and Tier 1 suppliers in the automotive industry to switch from wave soldering to press fit.
Press fit interface options
Press fit pins, also known as compliant pins, generally have an elastic cross section and a diameter exceeding PTH. During the assembly process, the press-fit area of the press-fit pin is deformed to create an interface with the rigid PTH. The press-fit pins are integrated into the automotive connectors and modules to provide greater tolerances for the PTH compared to non-compliant solid pins. Press fit connectors are available in a variety of sizes, shapes, styles and pitches, depending on the application, either in single pin or in any number of pins.
The flexible press-fit pin reacts at a speed close to the spring to help protect the integrity of the PTH. The hole diameter of the plated hole on the printed circuit board substrate is small. Therefore, the thickness of the plating layer directly affects the insertion force, and must be strictly controlled to achieve a proper pin insertion effect without causing excessive friction problems commonly encountered in the case of silver plating.
This allows for a permanent connection that is highly reliable and provides an impact-resistant, airtight interface without the risk of corrosion. The inlet angle is an important parameter that affects the insertion force and prevents PTH damage. The contour of the outer surface of the compliant area can also help to a large extent determine the insertion force and mitigate potential damage to the sidewall position.
Press-fit pin connections can be used on both sides of a printed circuit board for flexible two-sided through-hole and SMT printed circuit board assembly. Multi-layer stacked printed circuit boards may require plate-to-board press-fit tail plugs. In the ever-decreasing size of engine and transmission modules, press-fit pins can help protect sensitive components and save valuable space in a tight pin configuration. In smaller package applications, such as sensors and switches, press-fit pins are often molded directly inside the housing.
A particularly important point for automotive applications is to achieve a good balance between low insertion force and high retention. The economical "Eye" (EON) interface is a very popular, customer-preferred press fit style with excellent electrical contact and retention to ensure connection in harsh conditions.
Excessive insertion force
Tin whiskers:
On the surface of pure tin, stress promotes the growth of whiskers, causing short circuits between the tracks of printed circuit boards, jeopardizing the function of the module. Design guidelines for reducing tin whisker growth include reducing insertion force and reducing the thickness of the tin surface.
Jet effect:
The printed circuit board is mechanically damaged during the insertion of the press-fit pin. If the friction is too large, the surface will be scraped downwards to the front of the press-in direction, which will further aggravate the friction. The PTH will eventually be cut and pushed out to the bottom position. Reduce the insertion force to avoid jet effects.
Whitening effect:
After the press-fit pin reaches the final position, the structure of each layer of the printed circuit board will be pressed against the pin force. If excessive force is applied or the PTH is unstable, stress can cause partial delamination of the printed circuit board. After a period of time, the crack will cause moisture to enter, resulting in reduced isolation performance. Reduces insertion force and uses high quality printed circuit board products to reduce whitening effects.
Press fit material thickness, nominal printed circuit board aperture, mating blade width:
Press fit material thickness (mm) nominal printed circuit board aperture (mm) paired blade width (mm)
Thermal design advantages
Most automotive applications are classified as SAE Class 2 (105 ° C) for passenger compartment electronics and SAE Level 3 (125 ° C) for under-the-hood electronics. SAE Level 4 (150 ° C) classification applications are relatively rare.
If secondary soldering is required, the heat generated in the process can cause damage to the printed circuit board and the connected electronic components. The press-fit technology completely eliminates the excess thermal cycle, and the secondary connection in the assembly process can be achieved by applying force.
Technologies for emissions reduction and fuel economy, as well as in-vehicle electronics, navigation and safety functions, build up heat inside the engine compartment. The press-fit pin provides a highly reliable interface that naturally dissipates heat, has a much higher thermal threshold than a welded joint, and has a lower failure rate. Press fit pins are suitable for applications from low to very high currents without the heat build-up common in welded joints.
The press-fit pins do not require a high-temperature soldering process, there is no risk of solder bumps ejecting during the assembly process, and cold solder joints and flux residues are not present, which can potentially lead to short circuits or printed circuit board damage.
Migration to press-fit pin technology
In the process of moving from welding to press-fitting technology, it is important to work with experienced suppliers. Many factors affect the resistance of the press-fit pin, including material thickness, blade width, and PTH diameter of the printed circuit board. Even a slight change in the diameter of the plating layer can have a huge influence on the insertion force and the holding force. This type of change can determine whether a critical failure is constantly occurring or a high-performance connection is achieved.
In the process of continuous evolution of industry standards, the pin-to-pin technology achieved by the press-fit pin technology is becoming narrower and smaller, and the size is getting smaller and smaller, which is compatible with the trend of increasing density, electronics and electrification. Through universal press-fit technology, automotive manufacturers can achieve significant application advantages, save on printed circuit board assembly costs, while meeting stringent manufacturing requirements and global planning needs.
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