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1、Lead-Free Reflow Soldering Equipment Considerations无铅回流焊接设备的考虑事项Marc C. ApellDirector of Marketing - Thermal and Cleaning Systems市场总监- 热源和清洗系统It is clear that the electronics industry is on the move to lead-free assemblies. This trend is an effort to remove hazardous lead from electronic packages an
2、d reduce the dependency on lead materials that can leach into the environment during processing or eventual disposal. The effort to go lead-free is driven by environmental considerations, governmental legislation, and the marketing advantages of lead-free electronic packages. 显而易见，电子行业正在迈向无铅组装。现在的趋势
3、是努力去除电子封装上有害的铅和减少对铅的依赖，因为铅在处理过程中或最终废弃后会影响环境。环境保护的需要,政府法规的出台和无铅电子封装的市场优势推动了向无铅的转移。While there are many decisions to consider in the implementation of lead-free assemblies in the manufacture process, this article will discuss equipment considerations of reflow ovens and the ability to process quality
4、lead-free products. 在制造工艺中实施无铅组装时，需要考虑很多因素。本文将会讨论关于回流焊接设备及生产高质量无铅产品的能力所要考虑事项。Solder Pastes焊膏The first step in a companys lead-free initiative is the selection of solder pastes. While many types are available today, the biggest hurdle is finding a dropin replacement for current leaded materials used
5、today. The most dramatic issue facing solder pastes and reflow ovens is higher melting points, which make drop-in replacements for leaded materials difficult to find. To date, the most popular lead-free paste formulations include tin, silver, bismuth, and zinc. 实施无铅的第一步是选择焊膏。如今市场上有很多选择，最大的障碍是为当前使用的有
6、铅材料寻找到一个直接的替代品。焊膏和回流炉面临最大的问题是更高的熔点，这使得找到直接的代替品非常困难。至今，最普遍的无铅焊膏合金包括锡，银，铋和锌。The selection of lead-free solder pastes has also been a subject of many technical papers and extensive research. This research suggests that the most effective solder pastes have a melting point of from 217 C to 221 C. This r
7、epresents a large increase from the traditional eutectic lead pastes with melting points of 183 C. Due to component temperature issues, maximum peak temperature and maximum heating/cooling slopes tighten the reflow process window. 无铅焊膏的选择同样也是许多技术论文和研究的主题。研究提出最有效的焊膏熔点在217 C - 221C之间。相比传统的低共熔含铅焊膏的183
8、C熔点，温度显然有了很大的提高。由于元器件的耐温性能，最高峰值温度和最大升温/降温速率缩窄了回流工艺窗口。 Profiles温度曲线With the tighter limitations of solder paste specifications and the concern for damaging components at higher processing temperatures, we must look to different profiles and machine setups in order to utilize lead-free materials. Ther
9、e are two common types of profiles that are used in the reflow soldering process. They are commonly referred to as the soak and tent profiles (see figure 1). The soak profile is a process of subjecting the assembly to a temperature for a period just below the liquidous point of the solder to achieve
10、 a uniform assembly temperature. The tent profile is a continuous ramp of temperature from the time the assembly enters the oven until the assembly reaches the desired peak temperature. Desired profiles will differ based on the type of solder paste used within the building of the assembly. Depending
11、 upon the chemical makeup of the solder paste, the manufacture will suggest the best profile in order to achieve maximum performance. This information may be found by contacting the paste manufacturer. 由于焊膏规定的温度曲线范围更窄以及考虑到更高工艺温度上对元器件的伤害，为使用无铅材料，我们必须注意不同的温度曲线和机器设定。通常，回流焊接工艺中使用两种回流曲线，他们指的是浸润型和帐篷型温度曲线（
12、见图1）。浸润型温度曲线是在工艺过程中使组件板有一段时间能承受恰低于焊料熔点的温度，以达到一致板子温度。帐篷型温度曲线是从组件板进入炉子直至到达设定顶部温度连续不断的升温。理想的温度曲线根据组装中使用的焊膏型号不同而不同。根据焊膏的化学成分，制造商会推荐最佳的温度曲线以求达到最优的性能。具体信息可与焊膏厂商联络。 Lead-Free Reflow Profile Requirements无铅回流温度曲线要求Due to the higher melting points of lead-free solder formulations, the profiling requirements w
13、ill change a bit, thus requiring some changes in the setup of the reflow equipment. A change that is commonly overlooked is a “flatter” profile during the reflow of the solder. Due to the tighter process window, the peak temperature and TAL must be achieved without overheating the assembly or compon
14、ents. This requires a longer reflow zone and the ability to effectively transfer heat to the product. The issues can be solved by using two zones for the reflow requirement, or perhaps using a reverse spike in the reflow zone. With this method, the second to last heating zone maintains a process tem
15、perature higher than the last zone to drive heat into the product quicker. Then the final zone is used to sustain a uniform temperature in the assembly. 由于无铅焊膏合金的高熔点，温度曲线的要求有所改变，因此回流设备的设定也需要进行相应调整。一个通常被忽略的改变是焊膏回流中的“平坦”曲线。由于工艺窗口变窄，要达到峰值温度及TAL而又不能过分加热板子或元器件。这需要更长的回流区间和热量有效转移到产品上的能力。可以使用二个加热区作为回流区来解决这个
16、问题，或者在回流区域中使用峰值前移的方法。使用这种方法，设定倒数第二个加热区的温度高于最后一个加热区的温度,促使热量更快的传递到产品上。接着使用最后一个加热区来保持组装板上温度的一致。 Equipment Considerations: 机器需考虑事项Thermal Transfer 热量转移There are many concerns with the introduction of lead-free materials. In the case of reflow ovens and the requirement for higher process temperatures, it is assumed that a high temperature oven is required. This is not always the case. What is more i
