In the world, the main industrial countries are rapidly cut lead welding manufacturing process, including PCB components. North America, the European Union and Japan plans to use "lead-free" technology, many companies also as soon as possible to give up the lead welding process. Some companies take advantage of this situation, to strengthen the main means of lead-free technology as the consumer market.
To lead-free welding technology makes almost all aspects of the PCB components are affected, including testing and detection methods. Here, we discuss some related technical problems, as well as for lead-free welding automatic optical inspection (AOI), automatic X ray detection (AXI) and online testing (ICT) and other major impact testing and detection technology.
The concept of new welding technology
Prohibit the use of lead solder trend to promote the electronics manufacturers and industrial organizations, such as NEMI and IPC, began to consider changing the traditional tin lead soldering chemical method, to seek a new way. Teradyne participated in the formulation of Nemi "from America of lead-free soldered assemblies technology roadmap", "lead free components are mixed and repair project", and joined the IPC 7 32 welding detection capability Standards Committee.
The new concept includes the lead-free soldering tin silver copper and tin - copper welding technology. Most of the electronics industry with the behavior is to achieve lead-free soldering tin silver copper alloy family transformation. NEMI recommended for reflow soldering of Sn3.9Ag0.6Cu (+/-0.2%) and Sn0.7Cu for wave soldering "industry standard" lead-free alloy. However, with the change of many process, should be carefully considered, the proportion is more suitable, suitable for application to a wider range of the alloy is in line with the specified product marketing requirements, economical and practical.
reflux temperature
Lead-free soldering ingredients have a high melting point, may make the components and / or component damage. According to the concept of SnAgCu lead-free solder, melting temperature increased from 183 to nearly 217 DEG C, the peak temperature of 260 DEG C. Through a long time of pre heating can make the temperature properly reduced. Repair temperature is also affected, some parts of the repair temperature up to 280.
The components used in this high temperature must be qualified for manual assembly of the components that have not been certified.
Optical detection problem
Detection of lead-free solder is basically and the detection of conventional lead welding there is no difference. Lead free solder joint appearance looks very similar to the traditional tin lead solder joint. Detection of which type of welding, the key is to find the correct judgment of each form of visual characteristics of the detection mechanism.
However, there are still some differences between lead-free and lead free solder joints, which affect the accuracy of the AOI system. Lead free solder joints are more obvious, and are more rough than the corresponding lead solder joints, which are caused by the phase transition from liquid to solid. Thus, this kind of solder joint appears to be more rough and uneven. In addition, the surface tension of lead-free solder is higher than that of lead solder, so it is not easy to flow. These visual differences require re calibration of AOI devices and software. For example, there is a slight difference between the "auto pass value" in some lead welding AOI system and the lead free soldering.
If the current use of manual testing, and consider the conversion to AOI system, it is the right opportunity, because at this time the manual tester must be re calibrated".
Industrial research conclusions of lead free solder detection
2002 Tai Ruida company funded established national physical laboratory (NPL), of AOI system lead-free soldering detection capability were carried out to assess the independent. NPL is the UK national standard laboratory, is independent of the measurement and material science research, development and knowledge conversion center, in the international enjoys a high reputation.
NPL of lead-free surface installation component of automatic optical inspection system "this topic were studied and in July 2002 announced the findings and to determine if there are problems of lead-free soldered assemblies of automatic optical inspection system.
For the study of use of the test object is a special color component this study produced, once produced many, some have some defects, no defects. Components include many different types of welding. Each component contains nearly 100 elements and more than 1400 lead-free solder joints. The design of the element types include 0.4mm pitch 256 foot QFP 0.5mm, pitch TSOP, and 0402 resistance. The defect types include leakage welding components, misalignment of components, but the correct size parameter error components, bad solder joints, wrong polarity components, welding and welding bridge, uneven components etc..
Participate in the evaluation of AOI system with six different manufacturers, including teradyne. Use the same software algorithm for detecting component and conventional lead lead-free components. Research shows that the lead-free solder PCB results lead PCB and the same, or even better. The error detection rate of the two is very similar. Need to test times and test objects of lead is irrelevant.
Research shows that, although in different equipment test results are slightly different, but most of the AOI system can be used for the detection of lead-free surface mount assemblies. Some use color algorithm and system dependent monochromatic cameras will encounter problems in the assessment of lead-free solder joints when. Practice has proved that the AOI system used for welding analysis, does not need to use the color image, the monochrome image contains all the information necessary for the analysis of welding. But a better detection effect using color image defects such as lead-free solder defects, welding bridges and etc..