Reflow-soldering without gas pockets
The new Sony CMOS sensors with global shutter technology are raising the standards in industrial image processing. However attractive their technical image capabilities may be, they also create great challenges in the production of a high-quality soldered connection, due to their LGA package (Land-Grid-Array) with short distance to the PCB surface.
Since 2011, WEPTECH elektronik in Landau has been successfully using a special production technology, by which the Sony CMOS sensors can also be soldered onto the circuit boards, with only very small gas pockets in a cost-effective convection process.
Convection soldering with problems
In the conventional and cost-effective process for camera production, a machine mounts all electronic components, including the image sensor, onto the circuit board and puts – again performed automatically – the board in the connected soldering oven. This oven connects the components, using the so-called Reflow-Convection-Process, electrically and mechanically with the board. Because of the high automation expenditure, by this means it is possible to produce small or large batch sizes fast and cost-efficient. This can only be achieved by a sophisticated and detailed coordination of PCB surface, soldering paste and soldering profile. In a standard soldering process, the criteria of the often required quality standard IPC-A610 can hardly be achieved for the new CMOS sensors with LGA package, regarding voids in solders.
Alternative: Steam soldering with vacuum?
For extensive soldering joints, the vacuum-assisted Condensation Soldering, also known as Vapour Phase Soldering, is an effective process for the production of solder connections with hardly any gas pockets. This procedure is often used for performance components, where, besides the electrical connection, also criteria like heat conduction and current density play a role. Despite of optimized vacuum support, the high weight and short distance of the CMOS sensors to the PCB surface, lead to suboptimal soldering results. Although the volume of the voids drops to an acceptable size, even with fine dosage of vacuum, dispersion of solder cannot be completely prevented, due to sudden gas leakages out of the solder joint. The procedure also holds economic disadvantages, as the soldering systems are usually not integrated into the fully automatic production lines. The often manual handling increases costs.
Sustained quality in the economic process
With decades of experience in electronics manufacturing and continuous technical progress of production methods, WEPTECH has succeeded in developing an optimized Reflow-Procedure in the convection oven for components in LGA packages. The process provides reproducible, stable solder joints for the new Sony CMOS sensors with extremely low level of very small voids. Walter Quintus, Technology Engineer at WEPTECH, reveals just this much:
“Thanks to a special pretreatment and a new adjustment of the process parameters, the sensors can, in strict accordance with the manufacturer´s instructions, be soldered almost free of voids. This reproducible process is robust. The cameras, which were manufactured in many different lots, including intensive stress tests with climatic chamber, long-term operation and On/Off-operation prove that.”