SMD焊接作业(简)

壹 SMD焊接作业 1 Keep the circuit board clean Isopropanol or wood alcohol is suitable for removing light oils and grease PCB s should always be washed under warm water then oven dried at 60 degrees Celsius for 10 to 15 minutes Handle the PCB by the edge only and avoid touching copper with your bare hands 线路板保持干净 轻微的油渍可以使用酒精去除 冲洗 PCB 板务必要使用温水 然后 在摄氏 60 度下烘干 10 到 15 分钟 过程中务必只能手触板边 绝对不能手摸铜箔 尤 其是裸铜 2 Use the right soldering iron for the job You don t need to purchase a temperature controlled iron special SMT tip or SMT hot gas reflow station These tools might be used in industry but only to save time and increase reliability 使用正确的烙铁 一般SMD并不需要特殊的烙铁 温控 SMD专用烙铁头 或者是热气式 的焊枪 这些一般常见于工业生产用 这些工具只是可以节省时间及增加焊点可靠性 但 并非是非用不可的工具 All sorts of SMT soldering jobs can be done with the common Weller workstation The important point is select the right tip i e have several tips on hand As with any soldering job the general idea is to have the joint up to temperature and soldered in a few seconds Think about how much of a heat sink the joint will be and choose the tip based on that Use of larger tips should be limited to areas of large solid copper plane i e ground plane For all jobs except very very small parts I use a small tip as shown above With practice you will learn what tip suits you best 一般的烙铁就可以做SMD的焊接 重点不在烙铁 而是烙铁头 进行锡焊接的要点在于 接点的温度及焊接的时间 因此首先要想到的是焊接点上的吸热 并且继而想到要选 用什幺样的烙铁头 一般会选用大烙铁头无非是有很大的裸铜或者是接地面上的焊 点 只要有够多的经验并且注意细节 你很快就可以自己选用合适的烙铁头 一般烙铁就可以焊接 SMD 重点在于烙铁头的选用 貳 Use L M P Low Melting Point Solder if you are experimenting LMP solder is very similar to 60 40 solder except that it contains 2 Silver This Silver loading has two effects It lowers the melting point a few degrees and it reduces the rate at which component metalisation leeches into the solder itself 使用低融点锡 这种锡与60 40锡相同 只是另外加有2 的银 增加银有二个作用 一 是降低融点 另外一个作用是增加锡融解后的延展度 SMT resistors capacitors ferrite beads etc all make there electrical connections via metalised pads deposited on a substrate Alumina ceramic ferrite etc The metal used is often Nickel or a related alloy One problem with soldering the same joint several times is that each time the joint is heated some of the Nickel leaves the component and joins the solder The is called leeching Leeching is only a problem when the solder joint of a metalised component is heated several times Leeching occurs at a faster rate with standard 60 40 solder than what it does with LMP solder 不论是电阻电容或电感 这些SMD型式的零件 都是采用金属介质成为端点 使用的金 属介质包含镍合金等 这些零件端点上的镍合金经过多次焊接后 镍会游离出来在焊 点上 这称为LEECHING 一般使用60 40锡时很容易产生LEECHING 使用低熔点锡 可 以降低零件焊点上的LEECHING效应 The downside of LMP solder is that it is about 3 times the price of 60 40 solder and harder to obtain although sources of supply have been quoted at the back of this article 使用低融点锡的问题点在于价格 这种锡的价格大约是标准60 40锡的3倍 同时也不 很普遍 If a kit was being built where the component values are known then 60 40 solder will be fine If component changes are often and likely then LMP would be more advantages for a long term reliable solder connection 假如制程中的零件是就定位的 而且也不会常因为更换零件而做焊点的融接 则可以 使用60 40锡 假如焊点异动频繁 则以低熔点锡较佳 Some people use solder cream sold by various shops The advantage of solder cream is that it has more flux than regular solder The solder cream is made up of very fine balls of solder mixed with a water based flux 有些人会使用锡乳膏 锡乳膏的优点就是它含有较多的助焊剂 通常锡乳膏是由很 小的锡球与助焊剂混合而成 Unfortunately solder cream was never intended to be used with a soldering iron In fact because the solder sits in a water based flux solution the cream needs to be dried out i e the water has been driven off before the solder can be melted This can be done by moving the iron tip close to the joint for a few seconds prior to moving onto the joint 很可惜的是 锡乳膏通常不用于烙铁作业 事实上 锡乳膏是呈液态状 因此锡乳膏制 參 程需要烘干作业 也就是要在小锡球溶解前必须烘干 这用在烙铁作业时 可以先将 烙铁头靠近焊点几秒钟 先烘干锡乳膏 然后再将烙铁头碰触焊点 In experimentation quantities solder cream is only available as 60 40 mix In my opinion the SMT experimenter would be better off to use LMP solder and extra flux from a tube or a pen rather than solder paste It is a matter of personal preference If you like using the paste then go for it 一般而言 适合实验用的的锡乳膏只有60 40 但使用于实验桌上还是以低熔点锡乳 膏较佳 同时还需外加助焊剂 Use solder flux where possible One of the biggest problems with soldering SMT parts is that the amount of flux within the solder core is not sufficient for the joint Professional SMT manufacturers use solder cream and controlled temperature ovens However soldering iron temperatures are far less controlled and often the flux has evaporated before the joint has solidified leading to dry joint which is often dull in complexion 可能的话 尽量使用助焊剂 焊接SMD零件的最大问题点之一 在于焊接点上的助焊剂 量往往不足 专业SMD制程往往使用锡乳膏作业 并且使用温控回焊炉 采用烙铁的缺 点 就是温度不容易掌控 而且往往在焊点尚未就绪前 助焊剂已发挥殆尽 这就容易 造成焊点的假焊 Solder flux has other advantages Because of its liquid nature it increases the conduction of heat from the iron tip to the joint It also increases the surface tension of the molten solder which helps to achieve a reliable joint and minimises the chance of bridging finely spaced pins 使用助焊剂还有其它好处 因为助焊剂呈现出液态状 它有助于将烙铁头的温度传导 到焊点上 而且也可以将焊点上的表面涨力扩大 这可以提升焊点的可靠性 Flux has the disadvantage that it is generally sticky and can require special flux removers to remove Soapy water and ultrasonic baths are one solution but this requires a second wash in fresh water and a bake in the oven Flux can also carry contaminants which may effect circuits operating in the microwave region or circuits with very high impedance s especially in VCOs Some fluxes contain lead based chemicals and it is wise to use gloves to avoid direct skin contact 助焊剂也有缺点 那就是沾粘 而且还需要助焊剂清除剂才能清洗干净 通常清除助 焊剂是使用加入泡剂的水用超音波清洗 之后再用清水冲洗 然后烘干 另外助焊剂 也有碍于微波讯号的传递 尤其是碰到高阻抗讯号路径等 因为有些助焊剂内含有铅 化合物 因此处理作业上 要避免用手直接接触 Flux is available from several hobby shops and other outlets in syringe see Fig 4 and pen application form In general the use of extra flux makes SMT soldering much easier and increases solder joint reliability However you may not need it at all 店面上贩售的助焊剂 有条状有笔型 SMD焊接有赖于外加助焊剂 这不但有助于焊接 肆 的流畅性 也有助于焊点的可靠性 Use a good magnifying lamp or other magnification source SMT parts are very small SMT solder joints are at least four times smaller again Since its the solder joint that should concern you most especially if you want to build something reliable it is useful to have a source of magnification Some examples are shown in Fig 5 SMD零件很小 而且其焊点可能比零件小上4倍 针对SMD焊接作业 你的关注焦点应该 是在焊接点上 这幺微小的焊点 可能需要放大镜来帮你详细检查焊点 Most people with reasonable eyesight should be able to solder without magnification and check the joint under magnification later For those who have relatively poor eyesight like myself special jeweller s eyes that sit on the head can help Good lighting is essential 大多数人用裸眼就可以初步检视SMD焊点 但是要彻底检查还是要藉助于放大镜 当 然够亮的灯光环境也是必须的 Dont work in a cluttered space Give yourself room to move around and orientate the PCB so its easy to reach the joint your trying to solder 不要在碍手碍脚的环境中作业 要让身处环境自由自在 同时PCB板的移动或转动也 伍 必须要流畅 这才方便SMD焊接作业 Buy a good pair of tweezers You will be amazed how much easier SMT soldering becomes In fact out of all the equipment I have suggested I feel this is the most important Both soldering and de soldering will involve your tweezers so they are a worthwhile investment If possible get a quality set where the two ends meet together accurately 聂子也是不可少的工具 好的聂子可以让 SMD 作业如行云流水般流畅 我认为聂子 可能是所有 SMD 焊接作业中最重要的工具 不论是焊接上零件或是焊锡除零件 都 必须使用聂子 要选用精品级的聂子 选用时候要检查聂子尾端的结合性 越精确越好 The following technique should be used for soldering small SMT parts such as resistors capacitors inductors transistors etc with a soldering iron 以下是焊接电阻电容电感晶体管等SMD零件的要点 1 Add a small amount of flux to the area if required and add a small amount of solder to one pad 先在必要的地方施加助焊剂 然后在零件单端加上少量锡 2 Pick up component in tweezers making sure component is horizontal Alternatively just move the component until it is close to the final position 用聂子夹起零件 注意要水平摆放 移到就位处 3 Whilst holding the component with your tweezers melt the solder on the pad and move the component into position 一边用聂子让零件就位 一边用烙铁让零件单端焊接固定 4 Remove your iron but continue holding the component until the solder has solidified Check to see that the component is sitting flat on the PCB If not re melt solder whilst pushing gently on top of the component with tweezers 先移开烙铁但是聂子还不能动 让温降下来后才移开聂子 在等待时可以先检是零 件是不是平贴线路板 如果没有 要双手并用 烙铁与聂子协调好 直到零件平贴 5 Solder the other side of the component 焊接零件另一端或其它端 6 Re melt the first solder joint and let solidify This ensures both joint are stable during solidification 烙铁回到第一个焊点上 让零件接脚可以正常舒展 以防接点断裂 7 Check your work under magnification 陸 使用放大镜检视这些焊点 8 The joint should be shiny and concave If you added too much solder wick up with small solder wick and try again See followed Fig for joint quality 检视焊点应该光亮且呈现完美的弧度 如下图中间位置 IC s require a similar but slightly different technique 以下是SMD IC的焊接技巧 1 Add flux to the pads where the IC is to be soldered 在所有IC接脚的裸铜上追加助焊剂 2 Add a small amount of solder to one of the corner pin pads 在IC的端脚裸铜位置加少量锡 3 Line up the IC with the pads on the PCB Double check the IC orientation 检视IC的方向有无摆错 并对齐方向 3 Melt the solder with your iron and move the IC into position with your tweezers Let the solder solidify 固定IC的第一个脚 同时注意其斜对角上的脚位置是不是也对齐 4 Solder the diagonally opposite pin Check under magnification that all pins line up with there respective pads 焊接斜对角上的脚 如果这两脚精密对齐 其余脚位置也应该是对齐的 6 Solder the rest of the pins and check work under magnification 焊接其余IC脚 De soldering Small SMT Components 拆解小型SMD零件 1 Add excess solder to one side of the component 先在其中施加一些锡 这可以让烙铁离开后能维持更长的高温时间 2 Whilst the side with excess solder remains molten move your iron to the other joint and gently push the component off the pads 迅速把烙铁移到另一端 用聂子把零件移开 3 Clean up pads with solder wick 请除零件移开后在焊点上留下的锡渣 Note The trick here is make one side of the component a larger thermal mass 焊锡不足 焊锡不足 焊锡过量 焊锡过量 柒 and heat that side first This may not work for all parts especially those sitting on large ground planes 以上的关键要点就是加锡让焊点可以维持较长的锡溶解时间 所以选择焊点也很重 要 例如加锡的焊点可以选择接地面 或有较大铜箔面上的焊点 De Soldering Small Outline Integrated Circuits 拆解SMD IC零件 This technique only works for SO IC 50 thou spaced devices Smaller devices may require hot air for removal 以下只适用于SO IC封装 脚距过小的零组件 就必须要使用热气枪 1 Apply flux to the IC pins 在IC脚上加助焊剂 2 Use solder wick to remove as much solder as possible from each pin 用吸锡器把整排IC脚上的锡吸除 3 Thread fine enamelled wire under one row of pins 用细小的漆包线穿过IC 4 Secure one end of the wire on a nearby component i e Large Electrolytic 固定好漆包线 5 Starting at the loose end heat each pin and pull wire simultaneously Pull the wire as close to the PCB as practical As the solder between the pin and pad melts the wire will pop out and leave the pin standing free of the pad and bent up slightly 整排IC脚加温 一面拉漆包线来移除IC脚与铜箔间的接触 6 Repeat steps 3 to 5 for the other side 依步骤3到5进行IC另一边脚的移除 What parts can you recycle 哪些SMD零件可以回锅使用 Some SMT parts can be quite expensive when purchased in small quantities All sorts of SMT parts can be recovered from surplus and junk equipment providing it uses SMT parts of course It will not only save you money but give you good practice at de soldering If you use recycled components perform an electrical check on them Ceramic capacitors cause the most problems they crack easily Inductors transistors and resistors can all be verified for correct operation However excessive heat may damage but not destroy the device 有些 SMD 零件不容易买到 因此就会想到回锅使用的问题 要使用回锅的 SMD 零件 有个原则就是要检测是否正常 电容会是比较大的问题 因为三用电表不易检测 而电 感晶体管或是电阻就比较容易做检测 要注意的是高温对小型的 SMD 零件很容易造 成伤害 但是不容易从外型看出来 捌 Special Techniques 特殊技巧 Whilst the purpose of this article is to detail the use of SMT with soldering iron there are a few exceptions One of these is the use of hot air instead of a soldering iron Hot air SMD rework stations are very expensive but a much cheaper source of hot air is a Weller Pyropen with a hot air tip Usually used for heat shrink the hot air tip makes removing SMT parts a breeze albeit a very hot one Use of flux around the component to be removed will help the heat conduction into the part and the PCB One of the draw backs with this technique is that surrounding components may also become molten and may possibly be blown off their pads This is more of a problem in high density PCB s with very small components when your trying to remove a large component such as an IC This can be overcome by folding up a small piece of brass sheet to fit over the component in question The brass provides a heat shield and ensures surrounding components remain on their pads 本说明旨在如何运用烙铁进行SMD零组件的焊接作业 不过SMD焊接世界中 常会碰到 需要热气枪作业 但是热气枪作业台非常昂贵 因此这里提供一个特殊技巧 也就是 可以利用一般拿做热缩套管用的吹风机 来替代热气枪进行SMD的焊接作业 可以再 打算去除的SMD零件的焊脚加上助焊剂 这有助于焊点的吸热 使用这个技巧的缺点 就是旁边的SMD零件很可能也会无辜被吹落 尤其是SMD零件密集的线路板 如果有这 个问题 可以在不想被拔除的零件上覆盖一层青铜片 这可以隔离热气 以防零件焊 点受热溶解而掉落零件 用来吹热缩套管的热气枪 玖 Surface Tension Your best friend 表面张力是你最好的朋友 SMT is shrinking the size of component packaging at an alarming rate How does one possibly avoid shorting pins with spacings like 0 3mm or even less The answer is simple You don t What do I mean by this With such small pin spacings you would go crazy trying to solder each pin individually With the aid of flux you can increase the surface tension of solder to su