The Removal of Flux Residues from Printed Wiring Assemblies

印刷线材组件（PWA）制造的关键步骤是去除PWA表面的助焊剂残留物。这种清洁确保了PWA的电气性能和装配后涂层的附着力，方便了组装的测试和检查，并保持了基板的机械性能。这种清洁通常使用氯化氟碳化合物（主要是CFC-113）和轻醇（如甲醇）的混合物来完成。随着《蒙特利尔议定书》的出台，CFC-113用于微电子清洁的使用正在逐步淘汰。一种可能的清洁替代方案是利用层状液晶相构象中的非离子表面活性剂溶液在其相反转温度附近。这些溶液对极性、非极性和混合污染物（焊剂残留物可被认为是极性和非极性污染物的混合物）具有超低的界面张力。当表面活性剂和污染物接触时，这种低界面张力允许污染物发生快速、自发的乳化。表面活性剂溶液对极性和非极性材料表现出较低的界面张力，因此它们在PWA衬底上的接触角将非常低，允许快速渗透到组件下方。表面活性剂溶液对焊剂残留物具有高的增溶能力，因此许多板可以在不需要再生清洁溶剂的情况下进行清洁。本研究包括实验和理论工作，以研究非离子表面活性剂的片层和胶束溶液作为CFC-113基pwa清洁剂的替代品。工作将集中在PWA表面污染物去除理论的发展和表面活性剂溶液的微观结构与控制污染物去除的参数之间的关系。表面活性剂、污染物和底物的结构和组成，以及清洗液中化学添加剂的作用，将关系到清洗效果。研究了层状和胶束表面活性剂溶液，并评价了溶液添加剂对这些相的形成及其清洁能力的影响。还将研究从PWA表面去除污染物的控制步骤。

A key step in the manufacture of printed wire assemblies (PWAs) is the removal of flux residues from the PWA surfaces. This cleaning ensures the electrical performance of the PWA and adhesion of post-assembly coatings, facilitates testing and inspections of the assembly, and preserves the mechanical properties of the substrate. This cleaning is usually done using blends of chlorinated fluorocarbons, primarily CFC-113, and light alcohols, such as methanol. With the advent of the Montreal Protocol, the use of CFC-113 for mictroelectronics cleaning is being phased out. A possible cleaning alternative utilizes solutions of nonionic surfactants in the lamellar liquid crystal phase conformation near their phase inversion temperatures. These solutions exhibit ultralow interfacial tension against polar, nonpolar, and mixed contaminants (flux residue may be considered a mix of polar and nonpolar contaminants). This low interfacial tension allows rapid, spontaneous emulsification of the contaminants to occur when the surfactant and contaminant come in contact. The surfactant solutions exhibit low interfacial tensions against polar and nonpolar materials, hence their contact angle on PWA substrates will be very low, allowing rapid penetration beneath components. The surfactant solutions offer high solubilization capacity for flux residues, so that many boards can be cleaned without requiring regeneration of the cleaning solvent. This research includes both experimental and theoretical work to investigate the use of lamellar and micellar solutions of nonionic surfactants as replacements for CFC-113 based cleaners of PWAs. The work will focus on the development of both the theory of contaminant removal from PWA surfaces and the relationship between the microstructure of surfactant solutions and the parameters which control contaminant removal. The structure and composition of the surfactants, contaminant, and substrate, as well as the effects of chemical additives in the cleaning solution, will be related to the cleaning effectiveness. Lamellar and micellar surfactant solutions will be studied and the effects of solution additives on the fromation of these phases and their cleaning power will be evaluated. The controlling step in the removal of contaminants from PWA surfaces will also be investigated.