![]() Some manufacturers will also test for chemical residue during processing. Verify the quality of materials being used, especially solder masks, and solders that contain flux. Making sure your manufacturer also has a clean production environment with strong process controls is the second step to prevent contamination. Taking precautions to ensure that your skin or hair does not contaminate the board, and by processing your product in a clean environment is a good first step for avoiding these contaminations. Human handling also leaves oil from skin and cross-contaminated sources on PCBs which are particularly difficult to remove. Unfortunately, humans are a source of contamination, with skin cells and hair landing on boards throughout manufacturing, especially if they aren’t in a clean room. Preventing contamination is one of the best practices for you and your PCB design. They also burn off and reform frequently, so they are difficult to track down and diagnose. These little traces (called dendrites) create bridges that make shorts all over the PCB. When ions are left on your board, usually by an etchant or other chemicals, an electric potential can cause “reverse plating” that pulls metal away from where you want, and redeposits new “traces”-think of them like PCB gremlins only there to cause you trouble and strife in their tiny, damaging forms. Some contaminants will just burn off the board, but it’s hard to tell how bad it is when your PCB is smoking.Įlectrochemical migration: This is one of the biggest concerns. After chemicals are used for any process, the board needs to be cleaned to ensure that no residue remains on the board to contaminate the next stage of manufacturing. Etching is an obvious source of acids, but flux, electrolytic solutions, and water-soluble soldering can all leave chemical residue on the board after their application and use. Any impurity or foreign material is especially problematic for solder because it can cause tin whiskers, which will create electrical shorts between solder joints or into traces.Įtchant and Chemicals: If you look into PCB manufacturing processes, there are a variety of acids and potentially damaging chemicals that get used during processing. Residue from flux can also be left on the PCB and function as a contaminant. The stencil printer and PCB finish are also potential sources for picking up and spreading contamination to your solder joints. The solder paste itself should be fine if it’s purchased from a reputable supplier, but contamination can get into the paste during the application and reflow process. Solder Paste Processing: The solder paste applied to the board can also get contaminated. Some other process steps which are areas for contaminants are as follows: The areas around wire bond interconnects are especially vulnerable. The most is degradation and accelerated deterioration of metalized surfaces, polymers, and masks. Depending on the type of contamination, and where it happens, a variety of issues can arise. Contamination on a PCBĬontamination comes from anything in the environment that is additional and should have already been cleaned off, from skin oils to remains of solutions. Knowing what contamination is and how it comes about is the first step to avoiding it in your future processing and designing. On PCBs, contamination usually is more subtle-impairing PCB functioning, damaging insulation, and causing shortages-the end result is still just as unfortunate for your hard work. While contamination doesn’t always have as dramatic of a consequence as an explosion, they almost always have adverse and frustrating effects. Thankfully he wasn’t hurt however, several weeks of work were ruined all because he must have left a speck of something on his wafer between processing runs. After a few minutes, he pulled the fume hood shut and encountered a small explosion from incompatible chemical agents. One day, a student coworker of mine was hearing weird sounds while etching. Processing steps use a range of chemicals, and sometimes these chemicals would not be compatible. When I was an undergrad, I worked in a lab with a heavy emphasis on etching. Ensuring chemical compatibility isn’t always as straightforward as avoiding throwing oil on a fire.
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