Journal of SMT Article

REFLOW SOLDERING OF THROUGH-HOLE COMPONENTS

Author: Phil Zarrow
Company: ITM
Date Published: 10/1/1999   Volume: 12-4

Abstract: The rallying cry of manufacturing has been “do it cheaper, faster, better”. Consequently there is a constant drive to reduce the cost of the product. After the cost of material, the cost of manufacturing is usually the most significant area contributor to product cost. The SMT manufacturing process is constantly being examined for ways of streamlining assembly. Aside from faster (and hopefully accurate) equipment, elimination of process steps is a practical approach to the enigma. Each process step carries with it related capital costs for the equipment utilized as well as recurring costs for process material, support labor, equipment spare parts, and, of course, overhead such as floor space, power, and other utilities. In many cases, steps can sometimes be eliminated through incorporation of advanced SMT manufacturing methods. Bear in mind that alteration of the assembly process in such a manner will entail formal process development using designed experiments and statistical studies if the manufacturing process is indeed to be optimized.

One such process that is gaining increased interest is Reflow of Through-hole (ROT). Known also as Single Center Reflow Soldering (SCRS), Intrusive Reflow Soldering, Pin-in-Paste, and by other terms, it is simply the reflow soldering of through-hole components. It is a fact that for the majority of electronic assemblies, there will always be a few through-hole components remaining on the PCB amongst the surface mount components. Connectors, for example, for applications where robustness is required, as well as power related components, will continue to exist in through-hole configuration. Rather than subject these components to wave-soldering or, time consuming hand-soldering, why not reflow solder them alongside with the surface mount components in the reflow oven? Granted, some through-hole components will not be able to withstand the thermal excursions presented by the reflow cycle, however, many can. This will result in the elimination of the very costly and environmentally “unfriendly” wave-solder process.

ROT is by no means a new process. Various companies have been working with it for a number of years and many have incorporated it into at least a portion of their mixed technology (SMT and through-hole populated) assembly production. Among the more significant contributions through a detailed formal study of reflow soldering of through-hole components undertaken in 1986 by a major US electronic manufacturing corporation. Experiments were conducted to examine and define all of the critical operating parameters. The resulting processes have since produced hundreds of millions of solder joints over the past 10 years. There have been, to date, no documented field failures attributed to the use of the process and its associated variations. In fact, the process has maintained a consistent solder defect rate in the range of from 4 to 7 PPM.



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