设备化学曝光
设备化学曝光
By Bradley Smith
质量保证可靠性
Allegro MicroSystems, LLC
Introduction
Allegro™ MicroSystems, LLC (Allegro) manufactures semiconductor devices with standard internal aluminum interconnects, and with external copper terminations plated with tin. The silicon-based device is molded in a standard non-hermetically sealed epoxy package. Customers may wish to use Allegro devices in a wide array of configurations, applications, and situations where exposure of the Allegro device to environmental elements and humidity, chemical solutions, motor oil, transmission fluid, road salts, and
依此类，可能会发生。这些不同类型的Allegro器件的化学曝光可能会在某些情况下导致设备的腐蚀和失效。本申请说明讨论了可能导致设备从腐蚀失败的情况和应用程序的类型。亚博尊贵会员请参考yabo 11选5
，对于可能与焊接和封装有关的其他信息，包括应用笔记Soldering Methods for Allegro Products (SMD and Through-Hole), AN26009;Guidelines for Designing Subassemblies Using Hall-Effect Devices, AN27703.1;andGuidelines for Leadforming Using Back-Biased Hall-Effect Devices, AN296080。
非气密环氧包
A hermetic package in the semiconductor industry is a ceramic package that seals the active silicon device completely from any and all chemical entry. A non-hermetic package in the semiconductor industry is a plastic package (filled epoxy) that covers, but does not seal, the active silicon device from chemical entry. For example, dye penetration test exposure results show that penetrating dye can be found inside all non-hermetic packages, but not inside hermetic packages. This is because the bond of the epoxy to the external terminations (copper leads) is not entirely intimate and can leave a micro-capillary void at the interface that is enough to allow chemical penetration.
The possibility of chemical penetration to the silicon active device means that no warranty or guarantee is possible from Allegro for corrosion failure of the device. It is therefore the responsibility of the customer to use the device in such a way as to minimize or prevent exposure of the device to corrosive chemicals. Chemicals which have been found to be corrosive to the internal silicon active device are (but not limited to): chlorides, phosphates, strong acids, strong bases, automobile exhaust gases, motor oils, transmission oils, ice melting salts, human contamination, and other automotive fluids. Because of the numerous varieties of chemicals, constantly changing commercial formulations, and unknown environments in which the device may operate, Allegro does not and cannot test or qualify chemicals for corrosion potential. It is therefore the responsibility of the customer or end user to qualify the final configuration of the device in the actual application environment or simulation.
In figure 1, aluminum interconnects on the silicon device are seen to have been corroded away, thus electrically disconnecting the circuits, after exposure in the field to a vehicle transmission oil. The device was confirmed by FTIR analysis to have the transmission oil on the surface of the silicon device, proving that penetration of the oil was complete. The package containing the device was not overmolded or conformal coated.
减少腐蚀的潜力
通过消除这种化学品的使用并在我们的装置的应用或组装中取代非腐蚀性化学物质，可以保护Allegro设备免受暴露于腐蚀性化学品。例如，如果将设备焊接到电路板或其他焊接操作上，则所用的焊剂通量应该是含非卤化物的磁通。用于除去助熔剂残留物的任何化学物质也应该是无卤和无磷酸盐的（这包括许多有机溶剂和有机化合物）。
Using protective coatings over the package containing the device can also provide protection of the device from chemical exposure. Conformal coatings can be very helpful to prevent chemical entry into the package. Typically, conformal coatings are applied after the device package is soldered onto the circuit board, or wired or welded onto terminals, or mounted in an assembly. The conformal coatings can be sprayed, dipped, applied with a roller, potted, or injected onto and around the device. Note that a sprayed-on coating does not seal all surfaces completely because it is unidirectional and the underside of the device may not be sealed. Dipped or potted conformal coatings provide a better guarantee of complete sealing. There are hundreds of types and varieties of conformal coatings to choose from, the most common being silicone, urethane, and epoxy. These coatings can be heat cured, air cured, or UV cured.
进一步的保护可以用来保护井斜ce package in harsh environments by potting or overmolding with a plastic. This is typically done for Hall sensor ICs used in ABS, transmission, cam timing or other automotive applications. The device package should be fully encapsulated in the overmold plastic to provide a better seal from chemical entry. The raw material for the overmold should be of such a purity grade as to have low-ppm content of chloride and phosphate. A nylon (PA) type of overmold can present problems because it easily absorbs moisture which can accelerate corrosion. Specifically, a nylon 6 or 66 type is known to have severe problems with moisture absorption, while nylon 612 less so. A polyphenylene sulfide (PPS) does not absorb moisture much at all and can be a best choice for some types of applications. Any leads or terminations or wires emanating from the assembly should also be overmolded or sealed with secondary sealers, potting compounds or conformal coatings. In general it should be noted that plastics do not seal perfectly to other plastics. Also note that superglues (cyanoacrylics) are not recommended.
加速因素和涉及生产腐蚀故障的其他条件是时间，温度，湿度，腐蚀性化学品的浓度，腐蚀性化学渗透量进入电子包装，化学品类型和水分。人类污染在客户组装过程中直接处理设备也可能导致腐蚀，并且手套和面罩的使用是必要的，以避免在子组件或板安装过程中腐蚀源。Allegro采取了很大的步骤，以确保其制造和组装的每个阶段都可以防止使用手套，面部面罩和全头到趾洁净室礼服的污染。
In general, the more layers of sealing material that are used (providing a more tortuous path for any chemical trying to enter), the more the device is protected and the long term reliability increased. Thus the use of a conformal coating over the device followed by an overmold of plastic would provide far greater reliability from chemical corrosion than either a conformal coating or an overmold alone. The customer must choose the appropriate configuration for the expected application, exposure to corrosive chemicals and level of reliability needed.
腐蚀性污染物
被水浸出的各种污染可能的职业r over time, even in overmolded applications. During assembly processes, the high processing temperatures can accelerate leaching, but more significant are the long-term effects. This can lead to the formation of corrosive compounds after the end product has been sent to the field. Major contributors to corrosion are halide and phosphate compounds. Materials containing halides (chloride) and phosphates should be strictly avoided in the assembly process. This applies not only to fluxes, but also to solders and solder pastes, and to overmolding compounds. Of particular concern are Nylon (PA) overmolding compounds, which can be highly susceptible to moisture absorption. The best defense against such corrosion is to eliminate halides from all materials used in the manufacturing process. For example, higher-grade nylons typically have minimal halide content. Such efforts should be supplemented by regular vetting of all process stages to ensure that no sources of contamination have been introduced. Sources can include not only materials consumed in manufacturing, but also substances that can be conveyed on the persons of production workers. Face masks, gloves, and suitable gowning should be in use at all times. The customer’s assembly operations should also take precautions to prevent the contact of the devices with bare fingers and similar contamination. Note that finger prints contain salt (sodium chloride) which can be particularly corrosive.
保护终端免受腐蚀
该装置的终端（引线）是基于镀锡的铜，并且也受到腐蚀。铜可以通过酸，盐，磷酸盐和其他腐蚀性化学品腐蚀。类似的化学品也可以腐蚀锡。如果有足够的化学曝光，铜线引线和电镀可以攻击和溶解，产生开路，或者更温和的腐蚀的残留物可以在导电或从树突生长中产生短的导线之间提供泄漏路径导致设备的电气故障。腐蚀性焊剂通量如果含有氯化物或者如果在焊接后不彻底洗掉活性助焊剂，则可能是一个问题。焊剂类型的商业名称是“清洁通量水溶液”或“无清洁通量”。这两种类型的助焊剂都应从板上清洗，以防止任何残留物直接引起腐蚀或防止良好的涂层或包覆材料的良好密封。申请的环境可能会使盐，诸如自动变速器（ATF），发动机油，排气或其他化学物质的盐，汽车流体，所有这些都会随着时间的推移可能会攻击和破坏终端的完整性。因此，应注意共形涂层，灌封或用全卷化合物以及整个包装体封装。
汽车应用亚博尊贵会员
The use of Hall cell devices inautomotive applicationswhere exposure to road salt, ATF, manual transmission fluid, engine oil, other automotive fluids and lubricants, and exhaust gases is one of the most potentially corrosive environments. Experience in the field (with hundreds of millions of devices) has resulted in few corrosion failures over the years, with overall corrosion levels in the ppb (parts per billion). Great care should be taken to design, engineer and manufacture automotive assemblies so as to minimize the chance for corrosive elements to enter the device and destroy it. Allegro recommends that protective coverings such as conformal coatings, overmolds, potting, and others be used to help provide layers of protection in these corrosive environments. Of the conformal coatings available such as silicones, urethane acrylics, and epoxies, the customer must select a coating and means of applying it that gives the best reliability. Note that overmolding with nylons does not provide the best protection by itself because nylons soak up moisture and contaminants readily. That is why potting compounds may be a better choice, or if nylons must be used (nylon 612 is the best of the nylons), they should be used with a good conformal coating over the Allegro package and leads prior to overmolding. Or PPS may be used, which does not have the moisture problems that nylons have.
There are papers and articles in the literature clearly stating that ATF and other automotive fluids can corrode electronic devices. One such article is: “Improving Sensor Reliability”, J. Titus, Test & Measurement World, 3/1/2005. Another is: “Corrosion Studies of Copper and Aluminum Interconnects Exposed to Automotive Oils,” Toshiaki Ishii, Nobutake Tsuyuno, Toshiya Sato, and Mitsuhiro Masuda, IEEE Transactions on Components and Packaging Technologies, Vol. 29, No. 1, March 2006.
Conclusion
引用的论文表明,活性硅保监会uit is very susceptible to corrosion. The epoxy molding compound that Allegro uses to encapsulate the device offers a larger degree of protection than a bare silicon circuit, but it is not absolute. Further protection can be afforded by the use of additional overmolding (such as nylon or preferably PPS), potting (epoxy), or a properly applied conformal coating (sealing 100% of the surface area). Such protection can take the reliability toward the 0 ppm level goal that the industry is seeking, but cannot guarantee 0 ppm. In addition, extra protection could help reach the automotive industry goals of 10–15 years reliability. However, achieving a given reliability goal of the customer’s assembly is the customer’s responsibility, therefore Allegro assumes no liability for corrosion of its device in the customer’s assembly from corrosive chemical exposure while in the application.
Copyright ©2007-2017, Allegro MicroSystems, LLCAllegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current.
Allegro的产品不得在生活支持设备或系统中使用，如果可以合理地预期Allegro产品的失败会导致该生命支持设备或系统的失败，或影响该设备或系统的安全性或有效性。
这里包括的信息被认为是AC Cu率和可靠性。但是，Allegr亚博棋牌游戏o Microsystems，LLC对其使用不承担任何责任;也没有任何可能因其使用而导致的第三方专利或其他权利的任何侵犯。