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JANUARY 2018 I PCB007 MAGAZINE 39 and re-spools on a take-up spindle at the exit. The type and complexity of the product deter- mines the needs of the supply and rewinding equipment. Type of Chemistry and Equipment Compatibility Obviously, your equipment must be made to last for years of continuous use. The first con- sideration is chemical compatibility with the materials of construction. Many of these ma- terials are already well-known to equipment builders. For example, if you are etching with a chloride-based etchant, stainless steel is a poor choice—chlorides will immediately de- grade the surface and slowly (or quickly) de- stroy all your fasteners! For this reason, tita- nium fasteners are generally used, and sumps and other contact surfaces must be of non- reactive materials such as polyvinyl chloride (PVC) or polypropylene (PP). Other materials can be used as well. Conversely, stainless steel is a good choice for most resist stripping chemistries. PP can also be used for stripping; its heat limit is low- er than stainless, but it has other advantages. These include extreme chemical resistance (a very good property if used adjacent to a chlo- ride etcher), low density with high rigidity (so less weight), lower material and assembly costs, and it is available in different colors. The important consideration here is if you plan on using a chemical process that is not well-known in the industry, for example a pro- prietary product with unknown organics or other "secret ingredients" or an unusual acid combination, it is critical to understand chemi- cal compatibility when specifying materials of construction. Rather than guess, it is best to test construction materials being considered for chemical contact with some type of immer- sion testing. One month of testing in a test bed at the expected operating temperature using the exact process chemistry is a good starting point. Again, most commonly used etchants, clean- ers, and strippers and their compatibility with construction materials are well-known; with something unusual it is best to consult with both your chemical and equipment suppliers to prevent a potentially costly (or dangerous) mistake. Taking this a step further and finaliz- ing a process while testing different equipment configurations on-site at your supplier's pro- cess development lab will likely lead to a bet- ter purchase decision. It is also certainly worth determining what your supplier's support will encompass, both before and after the sale. Access to and use of their lab, as well as the willingness to process samples, is an indicator of their commitment to your success. Reliability and Maintainability No one likes unexpected shutdowns. Clean- ing and preventative maintenance are an un- avoidable necessity if you want your new equipment investment to last as long as pos- sible and produce excellent results every hour that it is in service. So it pays to consider where in your production schedule you will be doing monthly and annual maintenance. Equipment design will play a big role in how much time must be set aside to do this. It should not be necessary to hire a mechani- cal engineer to service your production line. In fact, many of the most commonly cleaned or replaced items should be serviceable without the use of tools, or at most a wrench or screw- driver. If it is too difficult to remove a part for cleaning, or to replace a high-wear item, it will tend to not get done until that dreaded unex- pected shutdown occurs. Your selected supplier should be able to show you just how easy it is to clean and main- tain your capital purchase. In addition, a sup- plier that can provide same-day shipping of re- placement parts, as well as schedule their own It should not be necessary to hire a mechanical engineer to service your production line.