Lead process and the difference of lead-free processes [circuit board processing in the production process]
Update date：2012-8-20
Many customers ask: "lead process and lead-free process that makes any difference," how the price difference is so large, have any effect on production in the end, today we explore this issue. A few decades ago, when the placement machine at that time are not what the concept of lead and lead-free, all lead the process, followed with the improvement of international environmental requirements, the state has begun to pay attention, so there will be a lead-free process, but the lead process still exists. Talk about so much in fact, a lot of people do not care, here are many people may be concerned about. Categories of lead-free processing features lead process characteristics Solder alloy solder alloy compositions have a variety of solder alloys to choose from, the current gradually agreed to Sn96.5Ag3Cu0.5 (SAC305); best reflow soldering and wave soldering choose with a solder alloy. But taking into account the costs, many manufacturers of wave soldering select Sn99.3Cu0.7 solder. The use of the production scene solder alloy caused chaos no matter what kind of welding method, the solder alloy has been used Sn63Pb37 will not cause confusion with the use of the production site solder alloy Confusion solder alloy solder alloy confusion, Some advocate the use of Cu mass fraction of 1% to 2% of the alloy, but the market has not yet such products solder alloy single Tin solder costs wave soldering and hand soldering tin line, raising the cost of 2.7 times. Reflow soldering with solder paste costs about 1.5 times the solder and low cost Solder alloy melting point temperature is low temperature high temperature 217 ℃ 183 ℃ Solder solderability good Solder joint characteristics of brittle solder joint, and is not suitable for handheld and vibration products solder toughness Solder / solder-side compatibility solder side can not be lead-free solder side of leaded The energy consumption of welding energy consumption regardless of the wave soldering / reflow / manual welding energy consumption more than 10 percent to 15 percent lower energy consumption than lead welding Equipment needs wave soldering need to add a new wave soldering machines do not need to (improve productivity exceptions) The number of reflow soldering equipment temperature zone to increase the flexibility of adjusting the reflow curve. Length of the furnace can also use multi-temperature equipment, and enhance the flexibility of the temperature curve adjustment Manual welding to replace the tip does not need replacement Printing / placement machine does not need to be replaced, but printing / placement accuracy demanding need to replace the The welding process water cleaning process is not recommended to use you can use The reflow soldering process window is small, the temperature curve adjustment more difficult. Solder voids are difficult to eliminate. Tin bad solder joint on the process window, the temperature curve adjustment easier. Good solder joint voids to eliminate solder joint on the tin better Wave soldering tin on solder joint is not good, need to speed up the cooling, the tin bath alloy impurity content detected frequent degree of increase, there may be a production site needs testing instruments solder tin is better, the tin bath alloy impurity content detected frequently not production site testing instruments Hand soldering tip loss accelerate the loss of the tip smaller PCB plate can follow the lead plate, the best use of high Tg laminates. High Tg sheet, plate costs increased by 10% to 15% plate without changing the Pad at Management way organic solderability protection (OSP), HASL ENIG, also can be used organic solderability protection (OSP), electroless nickel gold Characteristics of OSP pad formation, the printing process requires high PCB retention time is short, the plan calls for. Influential of the ICT test ENIG pad formation, printing processes do not ask PCB to save a long time, do not ask the plan. ICT test, there is the possibility of the "black disk" Components, heat resistance, heat resistance requirements of high heat resistance is not very high Solder side solderability requirements of high demand general Solder joint inspection rough appearance of the solder joints bright spot test is more difficult, easier to test "Popcorn" phenomenon due to temperature and moisture sensitivity of many IC's in the lead-free soldering will increase one to two grades. In other words, the support of the moisture control or treatment must be strengthened. For those small-volume users will have more serious effects. Incoming inventory time because many of the very small mass with care has a longer period of time. If the inventory of moisture facilities are not ideal, it must be assembled before baking dehumidification to prevent the "popcorn". Baking can solve the problem of "popcorn", but the baking process will exacerbate the oxidation of the device solder side, brought the difficulty of welding. A viable approach is to use an inert environment to bake, but equipment, consumables (inert gas) and greatly increase the moisture sensitivity of the cost of the IC as long as the attention and management can easily be controlled "Tombstone" The phenomenon is more serious in the lead-free technology. This is because the surface tension of lead-free alloy is a strong reason. The principle of the solution and lead technology, which is most effective DFM control device solder side and pad size, and both ends of the heat capacity. Secondly, through the process of adjustment to reduce the temperature difference across the device. Should note that, although the principle is the same, but the lead-free process window will be smaller, so the user must first ensure that the stove itself uses have the ability, that is, good heating efficiency and stability of airflow in the lead technical However, lead process window is wide, easy to solve "Holes" The phenomenon is not easy to completely solve the problem of tin-lead technology. Into the lead-free technology, this problem also with the increase of surface tension of lead-free alloy is more serious. To eliminate the problem of "holes", there are three factors must be noted; solder paste features (select Paste), DFM (device welded side structural pad and template opening design), and the reflow process (temperature curve setting). Control principles and lead technology is no different from the knowledge process window a bit smaller "holes" in the tin-lead technology is not easy to completely solve the problem Industry's most robust data reliability data, there are many unknown features or shortcomings did not find many of the reliability data have been used for many years
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