Copper Plating Thickness PCBs

Copper Plating Thickness PCBs Copper Plating Copper Thickness Reliability Printed Circuit Boards should be viewed as electronic real estate. Essentially, the reliability of the components that, combined with the PCB, make up your product is only as good as the foundation upon which they are assembled. Reliability Testing To ensure our customers receive product that is of world-class quality, we utilize inside and outside testing capabilities. On a daily basis we manufacture a test panel that includes all of our capabilities. Once it is complete, we steam age the panel for 8 hours, test for solder ability, cross section the entire size of the whole to verify plating quality, and then test for Ionic Contamination. This is done on a daily basis, but every year we fabricate a daisy chain test panel and send it out for High Temperature Storage (125 C), Temperature Cycling (-45 C - 125 C, 1000hrs.), and High Humidity (100%, 1000 hrs.). These samples must maintain less than 10% resistance and then they are micro sectioned to verify the visual characteristics. In addition to these tests, we perform extensive Ionic Contamination tests; solder ability tests, resistance to chemical tests, and Autoclave. High Reliability Printed Circuit Boards The Reliability of a PCB depends primarily on the copper plating thickness, the fine grain structure copper plating, and the ionic contamination. Copper Plating Thickness The key to ensuring a minimum plating thickness of 1 mil is to reduce plating variability as much as possible. Standard manual plating lines can have variability across a single panel of +/- 40%. Thus, if a certain point on a panel measures 1 mil of copper plating thickness, there is a distinct possibility that other areas can have as low as 0.6 mils of copper plating, thereby affecting the long-term reliability of the PCB. Saturn has designed and built it’s own automatic copper plating line with the intent of minimizing variability by optimizing every parameter there is to copper plating. The primary factors include: 1. We only plate panels one-high, as opposed to 2-3 panels high. 2. Anode-to-anode distance is 28 inches (maximum distance allowable for plating). 3. Water-submerged positive cathode contact. 4. Chemical-submerged anode bars for constant positive contact. 5. Eductor system that utilizes a high-volume chemical flow parallel to the panels instead of air to accomplish chemical agitation. 6. Mechanical agitation to allow chemical to flow through holes. 7. Dual sided rectification to equalize copper plating from one side of the rack to the other. 8. State-of-the-art rectifiers (two per rack) with 0.5% maximum ripple effect. 9. Positive Thumbscrew panel contact to racks. Fine Grain Structure Copper Plating Copper plating rates can be calculated through the relation of amps per square foot (ASF) and cycle time. The greater the ASF, the less the cycle time. The industry standard is to plate at 30 ASF so as to minimize the required cycle time to reach 1 mil of copper plating. However, this results in large grain structure copper plating that will not withstand thermocycling tests. Saturn has set up its lines to plate at 17 ASF, which results in fine grain structure copper plating, albeit at a much lowered production rate. However, fine grain structure copper plating has enhanced contraction and elongation properties that are critical to withstanding constant temperature changes. Saturn tests the reliability of its product by performing extensive thermocycling tests. Our product is exposed to a 1,000 cycle thermocycling test in which one cycle consists of the following: 1. Room temperature down to -40° C within 5 minutes. 2. Stay at -40° C for 25 minutes. 3. Increase temperature to 125° C within 5 minutes. 4. Stay at 125° C for 25 minutes. 5. Decrease temperature to -40° C within 5 minutes. After 1,000 cycles are passed, the PCB cannot have a change in resistance of greater than 10%. Ionic Contamination Since the industry is set up for 6.4 μg/in2, the equipment suppliers design to meet this specification. However, in order to meet stricter high-reliability requirements of 3.8 μg/in2 or less, Saturn designed and built its own equipment. Since the primary cause of ionic contamination is the flux used prior to the Hot Air Solder Leveling (HASL) process, the best way to reduce ionic contamination is to clean the PCBs aggressively. Furthermore , Saturn has worked with its suppliers to develop a flux that reduces the levels of ionic contamination on the PCB. A brief comparison of our custom post-cleaner to the industry-best is as follows: INDUSTRY BEST (2) 1/2" wide brushes 1 1/2 H.P. chemical and water pumps 1/2 gallon per minute nozzles All PVC, allowing maximum constant operating temperature of 120˚ to 130˚C 3 chambers SATURN (4) 1" wide brushes 7 1/2 H.P. chemical and water pumps 1 1/2 gallon per minute nozzles All stainless steel, allowing maximum constant operating temperature of over 180˚C 4 chambers