乡亲们
我有点 "小屋热"，所以想去Simon Pearce 吃午饭。那里的氛围总能让我放松身心，神清气爽。于是，服务员把我安排在一张可以看到瀑布的小桌子上。餐厅位于一座古老的磨坊里，瀑布的水流曾用来驱动纺织机。现在，它为发电机提供动力。
我刚坐下，就听到一位迷人的年轻女士欢快地叫我。
"罗恩博士，快来和我们坐在一起。"常春藤大学教授帕蒂-科尔曼惊呼道。
图 1.Patty Coleman 教授和一位同事正在进行审计。
帕蒂教授与玛吉-本森（Maggie Bensen）和苏-马奇（Sue March）坐在一起。应她们的邀请，我也加入了她们的行列。
"哇，我感觉像是在和皇室成员共进晚餐！"我调侃道。
The three looked a little confused, so I explained, “I followed your adventures in a two year series sponsored by Indium Corporation and iConnect007.”
我们聊了一会儿他们的冒险经历，最后，我问苏："你想攻读数学研究生学位，但我感觉你可能会攻读工程学研究生学位？
Sue 脸色微红，然后回答说："我喜欢数学，但为我推荐的课程非常理论化。帕蒂教授建议我把数学技能用在电子装配上。玛吉正在资助我去常春藤大学攻读工程学博士学位！"说到这里，她的声音有些颤抖，有些哽咽。
每个人都安静了一会儿，然后我们聊了很多，大家似乎都很高兴能互相取经。
最后，我问帕蒂："帕蒂教授，您多年来一直在帮助人们改进装配流程。您认为装配工可能犯的最大错误是什么？
她毫不犹豫地回答道："把焊锡膏当作商品来考虑"。
图 2.锡膏不是商品
"我同意！你能进一步说明这个想法吗？我问道。
Patty 拿出她的智能手机，放在桌子上。尽管如此，如果焊膏不好，就会毁掉整个智能手机。为了节省几美分而选择更便宜、性能更差的焊膏，很容易导致智能手机毁于一旦"。帕蒂停顿了一下。"苏，你为什么不告诉罗恩博士，焊膏必须具备多少功能才能实现成功组装？帕蒂指示道。
苏呻吟了一声，然后笑着说："帕蒂教授让我们背诵一篇你写的博文，罗恩博士。答案是 15。"
"我只依稀记得那篇文章。你说要背下来是开玩笑的吧？我问。
"好吧，"苏微笑着说，"让我们看看我是否说对了！
"Solder paste is not a commodity, and it is important to understand why. Solder paste is likely the most complex material used in any manufacturing process. I think most people know that solder paste is a combination of solder powder and flux. At first glance, it seems quite simple. However, even the solder powder is not a commodity. In superior solder paste, the powder size distribution is well controlled, the solder particles are spherical,and they are not oxidized. Poor solder powder has powder particles that are non-spherical and oxidized.
Many of you may be familiar with type three, type four, and type five powders. All of these powders have certain size distribution requirements. Superior solder paste will have powder sizedistributions consistent with their requirements. Starting with a poor solder powder makes guaranteeing the right powder size distribution difficult, and not all fluxes are equal.
The flux is a complex mixture of solvents, activators, gels, and oxygen barrier components. It has many important tasks to perform. The solvents dissolve the other chemicals while the gel compounds give the solder paste its rheological properties. The rheological properties are important for the first step in the PCB assembly process: stencil printing.
Rheological properties are the thickness or viscosity properties of the paste and must be just right to perform well. A solder paste must be thixotropic, meaning that its viscosity decreases sharply as the paste is forced through the stencil apertures, but the viscosity increases dramatically when the solder paste is at rest right after it's printed. The result is a crisp, sharp solder paste deposit that maintains its shape after printing.
Next, the solder paste deposit must maintain its shape and not slump. After the components are placed on the printed circuit board, they must be held by the solder paste. This property is called "tack". During the reflow process, the solder paste must dissolve any oxides on the component leads and PWB pads. This task is the main responsibility of the activators. However, the oxygen barrier chemicals must protect these newly oxide-free surfaces through the reflow process.
Of course, one wants to assure that the quality of the solder joint is acceptable, but long-term reliability is also a concern. The solder joint must pass thermal-cycling and drop-shock testing to assure mechanical reliability. In addition, an important thing to consider is thatall 15 of these features must be very good-to-excellent for a superior solder paste. If a solder paste is terrific at 14 of the 15, but was poor at, say, electrical surface installation, it would be unusable.”
"哇！"我回应道。我回应道。我感到非常荣幸和感动。
午餐后，我们互道祝福，并承诺保持联系。
干杯
罗恩博士
注：所有人物和常春藤大学均为虚构。帕里-科尔曼教授刚刚度过了 15 岁生日。西蒙-皮尔斯餐厅是真实存在的，也是我最喜欢的餐厅之一。
