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68 SMT Magazine • March 2017 by Dora Yang PCBCART When it comes to technology and quality, an SMT assembler's capabilities will be reflected when you go through the key elements in the SMT process. This article provides key points to consider in evaluating a PCB assembler, which allows you to test whether your circuit boards assembled in that factory conform to your re- quired standard. Among the key elements in evaluating SMT quality are solder paste printing quality, reflow quality, how to avoid misplacement of compo- nents, how to avoid manual placement, capabil- ities on stencil thickness calculation and modifi- cation, size of aperture, up-to-date equipment or instrument. Of these elements, the quality con- trol of solder paste printing is the most critical. If solder paste is badly printed, your circuit boards are incontrovertibly in low quality, whether component mounting is accurately completed and reflow temperature is suitably modified. After all, non-standard amount of printed solder paste is closely associated with quality of soldering. In terms of the other elements, the accuracy of the surface mounter has already achieved the required level and reflow temperature curves have been determined in advance, therefore few modifications are needed. To evaluate solder paste printing capability, there are two aspects to consider: solder paste quality administration capability and solder paste printing capability. Solder Paste Quality Administration High-quality solder paste relies on its brand and freshness degree. The freshness degree of solder paste has to be tracked starting from the time of warming up, to jar opening and stirring. Different manufacturers conform to different regulations stipulating that solder paste has to be used up within a certain period of time, oth - erwise it will oxidize and lead to insufficient sol- dering in the reflow process. Furthermore, signif- icant administration has to be implemented on solder pastes applied in stencil. Solder paste is recommended to be stored in low- Evaluating a PCB Assembler ARTICLE

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