Vapour phase soldering on flexible printed circuit boards

The paper presents experimental results about Vapour Phase Soldering on flexible printed circuit boards, where the standard Surface Mounted Technology process was used for investigation. Test boards were prepared from FR4 type Printed Circuit Boards and single-sided flexible polyimide substrates. Lead-free SAC305 paste and different chip size surface mounted resistors were used for the test assembly. The soldering was performed with heat-level vapour phase method in a commercial oven. The tests were composed of different board setups: where the FR4 or the flexible boards were soldered without fixtures, and where the flexible boards were supported by fixtures. The results were evaluated with X-ray microscopy, cross-section optical inspection (IMC tests) and shear tests. The conclusion reveals similar quality factors in all cases, rendering vapour phase soldering a plausible alternative reflow method for soldering on flexible printed circuit boards