Comparing infra-red and vapour phase soldering technologies on flexible printed circuit boards

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Dr. Géczy Attila
Department of Electronics Technology

Flexible printed circuit boards are often used nowadays in the electronic industry. It is worth investigating which assembling (soldering) method could serve with the best result; flexible boards have many possibilities for their usage as well. It is also interesting how could the quality of solder joints be influenced by the different types of soldering methods.

During my thesis I gathered information about the reflow soldering process, focusing on vapour phase and infrared soldering. Then I reviewed the parameters, functions and the working principles of the available instruments. Later I researched the literature on the structure and usability of flexible printed circuit boards.

The base of my thesis was an earlier executed experiment, where flexible circuit boards were combined with vapour phase soldering. After understanding the results, I planned a new experiment: comparing vapour phase soldering with infrared soldering on flexible and traditional FR4 boards.

During the test I measured and analysed all board's thermal profile. Than I investigated the emerged solder joints with the available methods to get the most reliable conclusion.

My most important experience was that using a supporting fixture in case of flexible boards is highly recommended because with these fixtures the quality of solders could be better. Using a solder mask is also important because the number of pad lifting failures can be decreased and the overall quality of mechanical fixing could be better. After evaluating the results I couldn't recognize huge influence of soldering technology, but there were little differences (thermal profiles, shear strength). Object of further investigations could be evaluating different supporting fixtures to optimize the size of them and define the best soldering setup for the case of flexible boards.


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