![]() ![]() Testing both SMT and THT is done with bed-of-nails test fixtures. Since it is more difficult for manufacturers to catch opens with ATE, some tune their process toward using additional solder to make the manufacturing process lean more toward shorts than it would if left in the neutral state. This typically results from insufficient reflow. When soldering using SMT technology, the most significant problem is likely to be an open connection. The bigger problem is that solder will bridge from one component lead to the next to create a short. Otherwise, the connection to the part is good. It’s tough to create an open connection in THT unless the flow process is not reaching part of the assembly there are contaminants on the assembly, or a lead on the part is bent during the insertion process. When assembly technology changes from THT to SMT, the fault spectrum tends to change from a predominance of shorts to a predominance of opens. Opens and shorts are the most predominant failure mechanisms for PCBs (Figure 1, see the August 2001 issue of Evaluation Engineering). The method of test fixturing can be impacted. THT and test? There are at least three, all having an impact on the testing process: So, what’s the big deal about the implication of SMT vs. Implications of Assembly Technology on Electrical TestĮlectrically, a component is a component, and automated test equipment (ATE) can test it equivalently whether SMT or THT attaches it to the board. Because of these reasons, it doesn’t appear that THT will be going away in the immediate future. Another strategy is to design circuit boards to accept both SMT and through-hole parts so that the most readily available parts can be used. With the recent industry-wide parts shortages, there have been reports of manufacturers redesigning SMT assemblies to be THT assemblies so parts can be purchased more readily. Parts are available in smaller quantities for THT (no need to purchase reels of parts).Īssembly of small lots is less expensive with THT than SMT. Simple circuits can be assembled less expensively with single-sided THT. The manufacturer doesn’t have SMT equipment to manufacture the assemblies. The circuit was designed prior to the advent of SMT.Ĭircuit components are not available in SMT. Many circuit assemblies still are being manufactured using THT. Is surface-mount technology (SMT) more difficult to test than through-hole technology (THT)? What roles do in-circuit testers (ICTs) and manufacturing defects analyzers (MDAs) play in testing these diverse technologies? Let’s examine the facts. To dispel some of the confusion, it’s important to answer a couple of questions. There are many misunderstandings regarding how the type of manufacturing technology used in the assembly of printed circuit boards (PCBs) relates to automated test. ![]()
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