EFFECTS OF AN APPROPRIATE PCB LAYOUT AND SOLDERING NOZZLE DESIGN ON QUALITY AND COST STRUCTURE IN SELECTIVE SOLDERING PROCESSESAuthors: Reiner Zoch and Christian Ott
Company: SEHO Systems GmbH
Date Published: 10/4/2009 Conference: SMTA International
Manual repair soldering that is expensive, time-consuming and cost intensive is already unacceptable due to the required quality and the reproducibility of the whole manufacturing process. In addition, densely populated multilayer boards and miniaturised, high-pin-count, fine-pitch devices cannot be efficiently repaired with high quality. "Hidden costs", such as productivity rates, operator training and damaged assembly costs have to be taken into consideration as well. Special focus has to be set to lead-free applications as manual repair soldering processes can cause enormous thermal problems.
The target, therefore, has to be a zero-fault selective soldering process.
An appropriate printed circuit board design is of the utmost importance here. For example, the shape of the pads and their distance in relation to each other can benefit – or with the corresponding design – exclude the formation of bridges. The distance between a pad to be soldered and an adjoining one that is not to be wetted, also plays a role.
The distance between the individual pins, as well as the length of the pins, are likewise to be taken into account.
Moreover, by choosing the correct soldering nozzle, one can avoid the formation of soldering faults in the automatic selective soldering process. The design of the soldering nozzle, as for example the shape or diameter, and the soldering nozzle technology used, such as wettable and non-wettable soldering nozzles, play a role here. Additional innovative features, such as debridging knives for example, can effectively avoid the formation of solder bridges, especially in the dip soldering process.
With many practical examples, this paper gives a detailed explanation of the individual points which should be found in the selective soldering process, with regard to the assembly design and solder nozzle technology.
Key words: selective soldering, board design, soldering nozzle design, cost reduction.
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