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How to prevent copper plating from breaking down in PCB?

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  • Wednesday, 06 June 2018

How to prevent copper plating from breaking down in PCB?

 Copper sulphate plating plays an important role in PCB plated, and it has a direct influence on PCB quality of plated copper mechanical performance and following process, so the key point of PCB plated is how to control copper sulphate plating’s quality, as it’s difficult for a lot of manufacturers to control the process. PCBGOGO makes a conclusion about the problem of copper sulphate plating for PCB plated based on years experience of plating and technology services as the following: 1). rough plating;2). plated shot copper; 3) plated pit; 4.)board whitening or different color and so on.

Rough plating: the reasons why there is rough board angle is that  plated  electric current is huge, and the way is to turn the current down and check if there is abnormal condition with pincers; there is rare condition in rough panel but also happened to customers as low temperature and insufficient light; and some dirty strip resist board also did.

Plated panel shot copper: there are so many factors in panel shot copper, such as immersion gold, the process of transfer pattern, also PCB plated copper itself. It can’t be denied that panel shot copper is caused by immersion copper as it’s happened to one manufacturer.

It may be any step of immersion copper treatment by which panel shot copper is caused immersion copper. It’s not only leading to rough panel, but is through hole as basic unoil has a good hardness in the water quality and much dust( especially not desmearing for double-sided board ) is bringing about bad filtering in the thrill; however, dot microetching and dirt could be removed in panel; there are some cases for microetching: the microetching hydrogen peroxide or sulfuric acid is bad, or the impurities of ammonium sulfate is too much, so it’s leading to defect expect industrial grade but at least CP grade; the reasons why copper sulphate crystals is separating out slowly is that it’s very high in microetching trough copper and low temperature; bath solution is dirty and polluted. Activator is almost result from pollution or maloperation, such as filtration pump blow out, the proportion of bath solution is low, copper content is high( the using of Activated cylinder is too long beyond 3 years), there will be granular suspended solids or impurity colloid in the bath solution to attract to the panel or hole wall with rough through hole.

Peptization or acceleration: it will be dirty as peptizer is making with fluoroboric acid, and glass fiber of FR-4 would be attacked to increase the silicate and calcium salt in the bath, also the panel shot copper is resulting from the increasing of copper and dissolved tin.

Copper sink itself is mainly caused by great activity in the path, its dust in the air-agitated, much small particles of suspending solid and so on, which it would be solved by changing the process, increasing or changing air cartridge filtration,and filtering the sank.So storing temporarily the diluted acid tank after immersion copper, keeping the path clean, and changing the dirty path on time. Immersion copper board is easily oxidize even in the acidic solution if it keeps for a long time, and it’s difficult for oxidation film to deal after oxidization, so shot copper is coming on the board.

Shot copper is distributing balanced with high regularity on the board expect because of oxidation, and it would result in shot copper of PCB plating copper whether the pollution is conducting or not, so it can be solved with soft brush for live defective board and taking some test board to do as treatment.

Pattern transferring progress: there is different oxidation on the board as developing has little glue, it’s not clean after developing, or panel is keeping for a long time after pattern transfer, especially under its bad cleaning or heavy air pollution for store workplace. So the solution is to improve wash cleaning, scheduling and acidic  disposing.

Acidic copper plating path itself, which can’t result in shot copper on the board for pretreatment as non - conductive particles is for skip plating or pits on the board. There are some points which shot copper is resulting from copper urn: bath parameter maintenance, manufacturing operation, material and processing maintenance. And bath parameter maintenance is including high sulfuric acid,low copper, low or high bath temperature, especially the factory without temperature controlled cooling system, at the same time it will make the current density decline, also it may be copper powder to mix with bath according to normal manufacturing process; there are some problems such as high current, bad cleat, empty grip, skip board in manufacturing operation, which make some boards with high current, copper powder, and shot copper; there is the problem of phosphorus copper keratin phosphorus and phosphorus with well-distributed in material; manufacturing maintenance is mainly in huge treatment, falling into shot as adding the copper angle, a lot of factories have trouble in treating anodic cleaning and anode bag cleaning. Cleaning the surface up and mircoetching with hydrogen peroxide, soaking the anode bag with sulfuric hydrogen peroxide, cleaning up,especially the anode bag is filtering with 5-10um is what the copper ball treating.

Plated pit: there are so many processes resulting in plated pit, which is from immersion copper, pattern transfer to pretreatment plating,plating copper and plating tin. Plating copper is caused by  dirty immersion copper basket for a long time, the pollution with palladium copper is dropping on the board to be polluted as mircoetching, and the point skip plating is what plated pit after immersion copper.And there are so many reasons that pattern transfer is mainly in apparatus maintenance and unclean developing, such as pollution glue stains with brushing machine, dry, dirty air knife and air blower, powder and oil pollution, board film or badly cleaning before printed, unclean developing, bad wash cleaning after developing, defoaming agent with silicon is polluting the board and so on. Pretreatment plating, which it’s sulfuric acid no matter what  acid degreasing agent, mircoetching, prepreg, path, so there will be dirty and polluted the board as high water quality; the non-conductive particles is attaching to the board surface and leading to different plated pits for the following plating.

Acidic copper plating path itself, which is mainly in some aspects: drum tube went off the original site, air agitation is not good,  filtration pump blow out or feed inlet intake air near by tube to be air bladder and adsorb in the board or line side; and another point is it’s not well treating with bad wick, the bath solution is polluted by destaticization leading to skip plating, which is increasing the inflate, clean the foam on time, wick need to prepreg with acid-base, and there is a question about the white board or bad color,which is mainly in light agent, maintenance, cleaning or mircoetching, and heavy organic pollution, high temperature for the path and so on. It won’t have any cleaning problem for acid disposing, but sometimes there will be bad cleaning and mircoetching if PH of water is acidic; and mircoetching is mainly in low microetching agent, high copper, and low temperature in the path and so on, which would be different mircoetching on the board; besides, slight oxidation is resulting from bad quality, long cleaning and  polluted acid prepreg, and different color is in acid oxidation and receiving tank with electricity,and difficultly quit the oxidation is leading to different color; and its defect is resulting from the board get to anode, bad conductive for anode, passivating anode and so on.

 

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