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October 2016 • The PCB Magazine 71 source of the particulate material was not evident. It is a known fact that anode sludge (forming on the copper anodes during plat- ing) can enter the plating solution and cause roughness. The question is how? It was sug- gested that the anode bags themselves (anode bags cover the anodes and are designed to prevent material from entering into the solu- tion) be inspected. It was noted that several of the anode bags had worn out significantly to the point of developing tears in the bags themselves. As a corrective action the anode bags were replaced with new ones. In addi- tion, improvements were made in the plating cell filtration. In this case, the 25-micron fil- ters were replaced with 5-micron filters. And the solution filtration rate was held steady at three solution turnovers per hour. The result was a major improvement in the quality of the plating coming out of cell #1. Summary This actual case study points out again the complicated nature of solving printed circuit board defects. In this case the defects were ex- ternal and could be readily seen after acid cop- per plating. However, the root cause analysis pointed out that the origin of the defects was from two different sources. And the trouble- shooting exercise dealt with each appropri- ately. PCB Michael Carano is VP of technol- ogy and business development at RBP Chemical Technology. To read past columns or to contact Carano, click here. CASE STUDY: PLATING NODULES—WHERE DID THESE COME FROM? To help imbibers easily and quickly know when they've had enough, sci- entists have developed a flexible, wearable patch that can detect a person's blood-alcohol level from his or her sweat. The moni- tor, reported in the journal ACS Sensors ("Noninvasive Alcohol Monitoring Using a Wearable Tattoo-Based Iontophoretic-Biosensing System"), works quickly and can send results wire- lessly to a smartphone or other device. Currently, ignition inter- lock devices are being marketed as a way to pre- vent drunk drivers from starting a car engine. But these are based on breath analysis, which can be affected by a number of factors including humid- ity, temperature and whether someone has used mouthwash. Recent research has demonstrated that sweat can be a more reliable real-time indi- cator of blood alcohol con- tent. At least two transdermal sensors have been devel- oped to measure alcohol levels in sweat, but users have to wait up to two hours for results. Joseph Wang, Patrick Mercier and colleagues at the University of California, San Diego, set out to make a more practi- cal version. With temporary-tattoo paper, a patch that tests BAC non-invasively in three rapid steps. It induces sweat by delivering a small amount of the drug pilocarpine across the skin. An enzymatic reaction leads to the electrochemi- cal detection of the alcohol content. And a flexible electronic circuit board transmits the data via a Bluetooth connection to a mobile device or lap- top. The steps take less than eight minutes from start to finish. Detecting Blood Alcohol Content with an Electronic Skin Patch

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