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DSM presents reflow best practices during 2019 Auto EPCON

22 May 2019
  • Candace Roulo Global Manager of Messaging and Content Development

The Society of Plastics Engineers (SPE) hosted its fourteenth annual Auto EPCON conference in Troy, Michigan, in May. Paula Kruger, application engineer for DSM Engineering Plastics, presented best practices for reflow of electronic components during the conference.

The theme of this year’s conference was “Pushing the Boundaries.” With the evolution of electric and autonomous vehicles, the automotive plastics industry is expanding into new applications.

Kruger’s presentation focused on electronic components—the reflow process and key material properties for success. As the integration of electronics into automotive continues, compact design becomes more important, and to ensure safe and reliable operating during the vehicle’s lifetime, several requirements must be met.

The example application discussed was an electronic control unit (ECU) for electric power steering. For this specific application, ForTii® T11, PPA-GF30 FR(40) was utilized in components such as lead frames and connectors. It is 30% glass reinforced, PA4T, electro-friendly, halogen free, red phosphorous free, and certified V-0 at 0.2mm.

Kruger spoke about the aspects of selecting the proper materials; industry standards that must be met; reflow soldering process; and thermal, mechanical and electrical properties.

At the beginning of the session, Kruger pointed out that the design of the ECU is very compact, and electronics are being squeezed into the smallest packaging space possible. “When working with compact designs, components like lead frames and connectors suitable to the reflow soldering process are needed,” said Kruger.  

Reflow soldering process

Kruger also explained the reflow soldering process and why there are concerns about deformation, fast moisture evaporation for materials that absorb moisture, and thermal degradation of the components.

“The European Union started banning lead in electronics in 2006 and since then lead-free solder paste is used—it melts at higher temperatures than lead containing paste, which means one must put the board through a higher temperature process to have this solder to reflow,” explained Kruger.

Materials properties and selection

As the bar is raised for lead-free soldering, only a few materials can handle this process, and PPA is one of them. However, there are some concerns about moisture and blistering. Blistering leads to irregular wall thickness that can cause potential mechanical and electrical performance issues.

ForTii has a high HDT compared to others, which means less risk of deformation when exposed to high heat for a short time. Regarding the mechanical properties, there is a good balance between tensile stress and strain, which is essential for design flexibility.

Furthermore, the high RTIs indicate good resistance to thermal degradation, and the higher CTI [low PLC] is desired for thin walls.


She also emphasized the importance of considering weld line strength and CLTE during the design process. “Typically, PA-based materials will present weld line strength in the rage of 40-50% of the strength of the original material,” said Kruger. “In the case of ForTii T11, the CLTE is important too, especially when connectors need to be exposed to testing and temperatures range from -40° to 150° C. Since this is such a wide temperature range there can be a lot of contraction and expansion.” 

Takeaways for design success

Kruger wrapped up her session with a list of key takeaways:

  • Thinnovation: UL V0 rating is at the smallest wall thickness in design.
  • Moisture and blistering: Most manufacturers look for a MSL1 or 2 approved materials. 
  • Materials properties for design:

            o   A high deflection temperature that is above temperature in reflow process.
            o   Mechanical strength and weld line strength (it doesn’t help to have a really strong
                 material when the weld line’s strength is very low).
            o   Long-term heat resistance for USCAR Class 4 in this application.    
            o   Comparative tracking index (CTI): A small PLC of zero will allow for shorter
                 distance between terminals.
            o   Coefficient of linear thermal expansion (CLTE): a good balance between parallel
                 and normal directions is important for performance of the part.  

To search for PPA materials, visit plasticsfinder.com. For questions or technical inquiries, visit dsm.com/contactdep.

ForTii: The best in class stiffness

   

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