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Vacuum boosts 3D vapor-phase soldering process

Posted: 18 Jun 2015 ?? ?Print Version ?Bookmark and Share

Keywords:moulded interconnect device? MID? vacuum? thermocouples? Galden Vapor?

A vacuum can be employed to achieve real advantages in the soldering process. We needed to take a closer look at the soldering process with vacuum profiles, so an evaluation project was performed. As a result of the uniform distribution of the vapor during the pre-vacuum phase, it was possible to significantly improve the 3-dimensional soldering process for a moulded interconnect device (MID) application.

Use of MID technology
MID technology is used in particular where significant miniaturisation, freedom of design with regard to geometry, and a reduced number of components for the electronics assembly is required. The electrical and mechanical features which are normally distributed to various components during conceptualisation and development are combined into a single MID part. And thus an intelligent, energy-self-sufficient pressure sensor system with a MID housing was developed as part of the Joint Project for Intelligent, energy-self-sufficient couplings for fluidic systems for automotive applications of the German Federal Ministry of Education and Research (No. V3EAAS010). Figure 1a shows the individual process steps required for LPKF-LDS technology in the production of the interconnect device. Thanks to the MID housing, the sensor could be made very compact and with a reduced number of components.

Figure 1a: The MID Housing Manufactured by LPKF-LDS Technology.

Figure 1b: The Vertically Distributed Mounting Levels of an Energy-Self-Sufficient Pressure Sensor

(source: Intelligent, energy-self-sufficient couplings for fluidic systems for automotive applications (IEKU, No. V3EAAS010), German Federal Ministry of Education and Research).

3D MID package
Due to the three-dimensional design of the housing, the contact points between the interconnect device and the PCBs are vertically distributed (figure 1b). As shown in figure 2, the package was soldered in the worst possible position for vapor phase soldering, namely as a cup. In conventional systems, this type of component positioning leads to excessive carry-over of the vapor phase medium. This results in some solder joints being heated more quickly than others, loss of medium from the system due to the cup effect C and a negative influence on the soldering profile. In order to investigate this effect, a soldering test was first of all conducted using a standard vapor phase process with a lead-free temperature profile.

Soldering test, vapor phase process without pre-vacuum
As shown in figure 2 (top), thermocouples are attached to various internal mounting levels, as well as to the upper and lower edges of the housing. First of all, the temperature profiles were recorded on the component while injecting the Galden heat transfer fluid at ambient pressure and followed by the main vacuum.

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