Precise and reliable mounting of electronic components using an optimized hydrogen vacuum reflow solder system
Fig. 1: RSS 110-S and RSS 350 hydrogen vacuum reflow solder systems.
Fig. 2: AlN submounts with solder preforms on top.
Fig. 3: Soldering fixture for assembly of optical and electronic devices.
Realization of high-end microelectronic devices is a process which consists of many sensitive fabrication steps. One of these steps is connecting the device parts by soldering. For this purpose, FBH uses hydrogen (H2) vacuum reflow solder systems to obtain the best results.
Main part of the solder system is the low vacuum chamber where solder processes are carried out flux free under H2 atmosphere. Preventing flux is especially advantageous for edge-emitting lasers and devices where the contamination with flux should be avoided. In contrast to liquid flux, using hydrogen reduces the metal oxides without residuals. Very good results in terms of surface wetting and bond quality are achieved.
However, atmosphere with high H2 concentration can be realized only in a closed chamber. This means that there is no opportunity to control or adjust the parts after they have been placed inside the chamber. Strong gas blasts during the process result in misalignment of the parts or even disassemble them from their proper positions. Especially light-weighted preforms can get in between the moveable hotplate and the cooling plate, thus creating a gap. This leads to a drastically reduced cooling capability and high repair effort.
Together with a system manufacturer the FBH achieved higher process stability through optimizing the gas injection system of the chamber. Hence, the positions of the parts to be soldered inside the chamber remain stable. This optimization reduces process times by 20% to 30% since a potential rearrangement step becomes superfluous. Parts are first arranged with an accuracy of less than 5 µm using an optical microscope and are subsequently placed into the chamber for soldering.
The optimized reflow solder system has meanwhile been connected to a Manufacturing Execution System (MES), allowing tracing and storing process data. This enables us to monitor and analyze these processes, permitting quick troubleshooting and adjusting of process parameter. In addition to the new H2 vacuum reflow solder system, a legacy solder system has been modified and reinstalled in our lab. Parts of the system were replaced and optimized to ensure secure operation. Furthermore, the capacity of fabrication has been expanded, therefore specialized solder and gluing processes are now possible.