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tech.com
The Benefits of Vapor Phase Soldering with Vacuum
By The Staff of Rehm Thermal Systems V
acuum soldering is primarily focused on removing volatile substances from solder joints
and reducing voids. Some reasons for this include increasingly strict requirements for quality and reliabil- ity of electronic products, as well as higher current densities (e.g. in power modules) and the resulting large power losses. Voids are gas bubbles that occur
due to outgassing from, for example, flux residues and byproducts of chemical interactions. Studies have shown that under pressure of less than 50 mbar in proximity to the molten solder is sufficient for a sig- nificant reduction in the number of voids.
Reducing Voids Figure 1 (page 90) shows high-
brightness LED solder joints after soldering without vacuum and a com- parison with vacuum. It is plainly apparent that with a vacuum of 10 mbar, the number of pores and their surface area is drastically reduced. In the event of solder joints with
large surface areas, as is the case with LEDs, QFNs and Si chips, a smaller number of voids results in improved thermal performance, as well as less tilting of the components. The permissible surface area in BGA solder joints occupied by voids
is the subject of much research. However, voids have not been shown to have any significant effect on the reliability of solder joints.
well, which may lead to increased formation of voids for design-related reasons and may be excluded from the 25 percent rule.
causes an increase in the void con- tent of the BGA, as opposed to a reduction in the void content of the QFN. These two types of solder joints differ from each other in particular with regard to their geometry and the surface area to volume ratio before and after soldering. Research results show that void
formation depends on many factors and that any lasting reduction of voids in solder joints can only be achieved with the help of vacuum. In addition to its primary objective of reducing voids, the use of vacuum also offers other advantages, which depend decisively on the technology of the equipment used.
Vapor Phase Soldering Vapor phase soldering technolo-
Rehm Condenso XC soldering system. This point is also made in vari-
ous standards, for example IPC-A- 610E. It states as acceptable, “25 per- cent or less voiding of any ball in the X-ray image area.” But, the use of vacuum soldering demonstrates a distinctly reduced void ratio in the case of microvias in the BGA pads, as
CONASHIELD “Flood Coat” Technology
Comparable Performance to Standard Potting Systems with a 30 to 60% reduction in weight
Better Electronic Insulation and Vibration Dampening Properties than Traditional Conformal Coating Systems
A True Balance of Properties Horizontal
Build 4-8mm
Surface Mount Components
Vertical Build 2-4mm
Circuit Board
TM Conflicting interactions are one
of the essential reasons for the fact that process and material optimiza- tions targeted at reducing the forma- tion of voids result in local improve- ment only (e.g. pertinent to only one type of component). Improved wet- ting of the immersion tin surface
gy is based on the principle of phase transformation (vapor liquid) and proper handling of the PCBs. Roughly speaking, we can differenti- ate between two principles: continu- ous boiling (vaporization) of the medium and injection of the medium into a thermally sealed process chamber with subsequent vaporiza- tion. In the case of injection, the vac- uum option is integrated into the existing process chamber. The heatable chamber of Rehm’s Condenso vapor phase sys-
Continued on page 92
February, 2020
Electronic & Engineering Materials
www.elantas.com/pdg See at IPC APEX, Booth 3823 See at IPC APEX, Booth 3523, and at ATX / MD&M West, Booth 1176 314.621.5700
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