无铅回流焊接设备的考虑事项

Lead FreeLead Free ReflowReflow SolderingSoldering EquipmentEquipment ConsiderationsConsiderations 无铅回流焊接设备的考虑事项无铅回流焊接设备的考虑事项 Marc C Apell Director 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 and 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 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 SolderSolder PastesPastes 焊膏焊膏 The first step in a company s lead free initiative is the selection of solder pastes While many types are available today the biggest hurdle is finding a drop in replacement for current leaded materials used 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 represents 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 221 C 之间 相比传统的低共熔含铅焊膏的 183 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 ProfilesProfiles 温度曲线温度曲线 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 There are two common types of profiles that are used in the reflow soldering process They are commonly referred to as the soaksoak and tenttent 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 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 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 浸润型浸润型和帐篷型帐篷型温度曲线 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 FreeLead Free ReflowReflow ProfileProfile RequirementsRequirements 无铅回流温度曲线要求无铅回流温度曲线要求 Due to the higher melting points of lead free solder formulations the profiling requirements will 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 components 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 temperature 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 EquipmentEquipment Considerations Considerations 机器需考虑事项机器需考虑事项 ThermalThermal TransferTransfer 热量转移热量转移 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 important is the efficiency of the machine to transfer the energy to the assembly 引入无铅材料要考虑到很多问题 依据回流炉和更高的工艺温度要求 便认为需要高温的回流炉 事实有时并不是这样 更重要的是机器转递热量到组件板上的效率 The recent release of the OmniExcel series of reflow systems from Speedline Technologies Inc includes innovative new heat transfer concepts to enhance heat transfer capabilities by enveloping products in evenly mixed process gas The heat on intake design allows for three independent zone intakes for process gas mixture Speedline Technologies 最新发布的 OmniExcel 回流系统系列中包括了创新的热量传递概念 将 均匀混合的气体混合物包围住产品来增强热量传递能力 进风口处的加热设计允许三个独立的区域 吸入空气进行混合 The center intake utilizes a finned rod heating element with over 900 square inches of surface area for thermal transfer from the heater to the process gass This approach allows for a reduction of heater wattage that directly translates to reduced power consumption This heating design has reduced power consumption up to 50 over traditional reflow solutions 中央的进风口使用一个表面积超过 900 平方英寸 鳍片形的加热器单元将热量从加热器传递到空气 这个方法可以减少直接传递热功率以减少能源消耗 与传统回流解决方案相比 这个加热设计已减 少了超过 50 的能源消耗 The gas heated by the heater elements is mixed through the blower unit and creates a mild back pressure behind the pressure plate This mild pressure behind the diffuser plate creates concentric circles of air that evenly overlap at the process level for excellent thermal transfer to the product Another design benefit is the exceptional zone to zone segregation of the heated zones for better control of the thermal profile of products being processed 被加热单元加热的气体由风机混合 在压力板后面产生适度的背压力 扩散板后适度的压力产生空 气的同心圆 均匀地重叠在制程面上 为产品提供极好的热传递 另一个设计优点是加热区之间的 隔离异常好 可以更好的控制产品制程温度曲线 Cooling the product is just as important as heating in reflow Extended periods above liquidous times and extreme peak temperatures can cause damage to the product and components Systems must be designed with recipe controlled cooling parameters In the case of nitrogen systems a chilled medium such as water is the preferred choice for cooling the process gas for the removal of heat from the product The chilled water design system should also allow for easy access in the design In one example the heat exchangers in which the chiller water passes are mounted vertically to allow any flux contaminates to drain naturally via gravity into a flux collection jar Water connections are made easy through connection points that allow a tool free removal Reflow systems considered may be designed with full access to the cooling without the opening of the heated chamber This in turn allows quicker scheduled downtime for maintenance and less energy required to return to operating temperature 回流焊接中产品降温如同升温同样重要 延长液态温度以上时间和极端峰值温度会导致产品和元器 件的损伤 系统必须按控制冷却参数方案进行设计 在使用氮气系统 冷却媒介如水是冷却工艺气 体 带走产品热量的理想选择 冷却水设计系统需要在设计中容易实现 举例来说 冷却水流经的 热交换器被垂直放置 使残留的助焊剂随着重力自然排入助焊剂收集瓶中 水连接可以通过快速接 头实现而无需工具 回流系统的设计应考虑可以独立操作冷却系统 不用打开加热的炉腔 这样可 以更快的设定维护保养的停机时间 减少回到运行温度所需要的能量 NitrogenNitrogen 氮气氮气 The benefits of nitrogen in a reflow environment have been widely debated over the years With the introduction of lead free pastes this is again becoming a factor 许多年来 氮气在回流环境中的好处被广泛地争论 随着无铅焊膏的导入 这再一次成为要素 Nitrogen serves a couple of purposes in a reflow environment The use of nitrogen protects board surfaces through multiple reflow passes prevents oxidation of pads and leads allows better wicking of leads and produces shiny solder joints This is most evident in the lead free process Higher lead free temperatures will act as a catalyst for the process of oxidation Nitrogen will act as an insurance to protect against oxidation Although not required for lead free processing nitrogen will allow wider process windows and many lead free reflow producers use it Nitrogen reduces surface oxides and allows better wetting of solder joints 氮气在回流环境中用于不同的目的 它可以保护板子表面通过多次回流 防止焊盘和引脚的氧化 使得引脚的浸润性更好 焊点更为光亮 这些在无铅工艺中更为显著 更高的无铅温度加速了氧化 氮气将起保护作用防止氧化 虽然它在无铅工艺中并不是必需的 但氮气的使用增大了工艺窗口 许多无铅回流生产者正在使用它 氮气可以减少表面的氧化 使得焊点获得更好的浸润 Reflow systems that are designed for either in air or inert configurations is an excellent choice when considering a thermal sytstem Balanced air flow within the heated zones translates into lower nitrogen consumption with the reduction of turbulance within the oven Time should be spent on the thermal transfer design and concept with the manufacturer to consider the balance of air flow The combination of closed loop blower control and variable speed blowers incorporated into reflow system designs enhance the performance and decrease nitrogen consumption 当考虑回流设备时 兼顾空气或惰性气体配置设计是非常好的选择 加热区平衡稳定的空气气流减 少了炉子中的紊流降低氮气消耗量 时间应该花在热量传递设计和制造商考虑的气流平衡稳定概念 上 闭环风机控制和可变速风机技术同时用于回流系统设计既可增强性能又可减少氮气消耗量 However the use of nitrogen can have a downside This includes initial cost of equipment the cost of nitrogen and the extra machine maintenance required on the reflow machines due to the flux volatiles trapped in the machine When reviewing reflow systems and the use of nitrogen an efficient system design should be considered 然而 使用氮气也有不利的一面 它包括机器的初始购置成本 氮气成本及因收集机器内挥发助焊 剂而产生的回流设备额外维护费用 回顾回流系统和氮气的使用 需要考虑高效的系统设计 VolatileVolatile ManagementManagement 助焊剂挥发管理助焊剂挥发管理 Another factor to consider is flux volatile management The oven should allow for a scrubbing of flux laden gas in a remote chamber and the return of clean gass to the process chamber 另一个需要考虑的因素是助焊剂挥发管理 炉子应可以在炉腔外净化饱含助焊剂的气体 再将干净 的气体重新送回炉腔 One example recently developed involves a patent pending two stage filtration separation system and incorporates self cleaning to reduce maintenance requirements The first stage utilizes a mesh strainer contained within a housing Upon entry into the housing the flux vapor undergoes an expansion increasing the pressure creating liquid droplets which if large enough will fall out of the air stream The remainder of the vapor is passed through the strainer which separates the larger heavier particles out of the vapor These particles mainly consist of any entrapped metals resins and rosins and they remain attached to the outside of the strainer This portion eliminates the build up of the highly viscous sticky and difficult to clean residue downstream in the system 有一个例子是最近开发的正在申请专利的二级过滤 分离系统 该系统结合自清洗功能以减少维护 第一级利用箱中的网状过滤器 助焊剂汽体进入箱体 开始膨胀 从气态变成小液滴 一旦增大的 一定程度 它将脱离空气气流 汽体的残留物经过过滤器 分离出大的且重的颗粒 这些粒子主要 包含收集的金属 松香和树脂 它们附着在过滤器的外部 这部分排除了高粘性及难清洗往下流淌 残留物在机器内的形成 The cleaning of this strainer is achieved through the periodic spinning of it via an attached motor The centrifugal force exerted on the particles overcomes the adhesion force attaching them to the strainer and the particles are thrown outward to the walls of the housing Since this system does not incorporate active cooling the entire system remains warmed by the chamber gases passing through This allows the heavy liquids attached to the walls to run down to the drain jar at the bottom of the housing 通过机器附带的马达定期的转动实现过滤器的清洗功能 离心力克服了粒子在过滤器上的黏附力 将其向外抛甩到箱体壁上 因为这个系统没有冷却功能 整个系统由于热的炉腔气体经过而保持热 度 这使附在箱体壁上的重液体 跑 入箱体底部的收集瓶 The second stage consists of a packed bed of stainless steel balls contained within a housing The small lightweight particles consisting mainly of alcohols and solvents contained in the vapor after passing through the first stage are again subjected to an expansion which increases droplet size The vapor then passes through the packed bed making multiple collisions with the steel balls Since the liquid contained within the vapor will spread out on the surface of the steel balls these balls are determined to be wettable Therefore upon initial collision of the particles with the balls heterogeneous nucleation occurs and the balls become covered with a film of liquid Once the balls are completely covered by the film the particles within the vapor collide with this film of liquid Since these are like substances homogeneous nucleation occurs and the liquid builds up forming droplets that are allowed to flow into a flux collection jar for easy removal 第二级在箱体里铺满不锈钢球 那些主要含有酒精和溶剂 包含在经过第一级的汽体中的既小又轻 的粒子 再次开始膨胀成液滴状 汽体经过底部与钢球发生大量碰撞 因为汽体中包含液体 它 将蔓延到钢球的表面 这些球被开始浸润 因此 在颗粒与球的最初碰撞上 产生不同质的晶核现 象 在球上覆以液膜 一旦球完全被液膜覆盖 汽体内的颗粒与这些液膜继续碰撞 因为这些就象 物质 形成同质晶核 液珠形成液滴 流入助焊剂收集瓶 非常易于清理 EnergyEnergy EfficiencyEfficiency 能源效率能源效率 Reflow ovens present one of the greatest concerns regarding power consumption in an electronics manufacturing environment This is understandable due to the nature of the process of transferring heat to product then expending energy to remove heat for the cooling cycle Efficient heat transfer techniques must be considered in reflow equipment design to deliver proper reflow profiles for leaded and lead free processing But it becomes even more important in the consideration of power consumption 关于电子制造中的能源消耗 回流炉是最受关注设备之一 这很容易理解 因为把热加载到产品上 是工艺过程的特征 再使用能量进行降温 在为有铅及无铅工艺提供适当的回流曲线的回流设备的 设计中必须要考虑高效的热传递技术 但基于能源消耗的考虑 变得甚至更为重要 Compared to other legacy reflow products tested there has been a tremendous improvement in the thermal efficiency and reduced power consumption by improved heat transfer capabilities and improved airflow with newer system designs Legacy reflow systems tested averaged 21 kW per hour running a leaded reflow profile under idle conditions Compared with recently introduced reflow systems power consumption was reduced from 21 kW per hour to 12 2 kW per hour with the new system design This is a 41 reduction in power consumption for similar profile performance 同其他流传下来 经测试的回流产品相比 通过改善热量传递能力及在更新的设备设计上改进气流 热效率和减少能量消耗有了巨大的进步 原先的回流系统的测试中 在待机状态下运行有铅曲线平 均每小时耗电 21KW 与最近推出的回流系统相比 由于采用新系统设计 能量消耗从原来的每小 时 21KW 降到每小时 12 2KW 相似的曲线性能下节省了 41 能量 ConveyorConveyor ConsiderationsConsiderations 传输系统考虑传输系统考虑 As product technology and production demands increase so do the demands and requirements of the reflow oven s transportation system Various conveyor systems and options are available to meet these demands the most basic of which is a simple mesh belt conveyor system 因产品技术和生产要求的提高 回流炉传输系统也需改进和提高 不同的传输方法和选项可供选择 以满足这些要求 最基本的是网带传输系统 Conveyor rail systems are the most popular method to transport electronic assemblies through a reflow system With the higher operating temperatures of lead free processing there is a concern for the ability for the conveyor rails to maintain strength Exposed conveyor support shafts and small rail profiles may be taxed at the higher operating temperatures and assemblies with higher mass Proven rail system designs allow for thermal expansion and maintain a parallelism of the rail system reducing the opportunity for PCB drop or jam within the system The rail extrusions may have multiple angles incorporated in the design to reduce the opportunity for rail twisting during the thermal expansion process 轨道传输系统是运送电子组件板通过回流系统的最普遍的方法 由于无铅工艺中更高运行温度 需 要关注的是保持轨道强度的能力 暴露的轨道支撑轴和小轨道结构可能在更高的运行温度和大规格 组件板下承受更重负担 成熟的轨道设计允许热膨胀且保持轨道系统平行 减少 PCB 掉落或卡塞的 几率 设计中融合有多种角度的轨道挤压构造 能在热膨胀过程中减少轨道弯曲 Due to the higher process temperatures in lead free reflow electronic assemblies may be more prone to warping and board drop issues Higher reflow temperatures are closer to the transition stage of the board laminate and combined with more mass from compon