It may seem obvious that we need dimensions on an engineering drawing to specify a solder preform, but we often receive drawings with missing dimensions or tolerances. I’m guilty of that too – especially with more complex drawings. Missing dimensions can be resolved, but checking for this before you send the drawing can save time.
另一方面，公差通常是一个更难解决的问题。在所有制造领域，机械师通常都希望获得更宽的公差以优化生产，但 "需要多大的公差 "这个问题却很难回答--尤其是对于新制造的产品。有时甚至不知道公差限制是什么。如果没有可用的公差，我们会让客户自己猜测，但我们会提供一套标准公差作为建议。如果公差不是很重要，在打印件上注明 +/-0.005" 的通用公差通常是非常安全的。
Omittingunits of measure may be the most frequent error we find on solder preform drawings. There can be no guessing here – since the dimensions in millimeters are grossly different than those same dimensions in inches. Again, a simple note “Unless otherwise specified, dimension are in inches” (or mm) can be quite helpful. Mixed units should be avoided, but can be used if there is a need for them.
One thing to note about pure indium preforms: tight tolerances are often not needed. In compression, pure indium is so soft that it will slightly elongate in the x and y axis as it is compressed in the z axis. During reflow, the pure indium will be flowing even more. Slight variations in length, width, or thickness will not make much of a difference in the final assembly.
