Lead-free tin boards ( Circuit board) The tin bad reasons

by:Rocket PCB     2020-06-26
Believe play most of the SMT process friend in solder, encounter this kind of SMD parts will begin to doubt whether the most for solder paste ( solderpaste) Printing bad ( The thickness of the steel net, opening, pressure, etc. ) , solder paste, SMD parts feet overaging oxidation, or reflow soldering temperature curve is not good. In fact, there is another reason that nots allow to ignore, is from the tin tin circuit board thickness of before you should be familiar with are gold ( ENIG) The gold layer and the thickness of the nickel layer will cause soldering problem, but tin boards ( Circuit board) The tin layer is too thin will cause bad soldering? The following are some of the books collected data, for your reference. Lead-free tin ( HASL) Tin bad case analysis on HASL boards ( Circuit board) The second face board after reflow solder bad reasons. Metallographic analysis, the result of the show doesn't eat soldering pad where copper tin completely alloying phenomenon, have this kind of copper tin alloy has been unable to provide solderability. Examine with batch no soldering PCB empty plate and slice analysis, found that without welding circuit board ( Circuit board) Welding mat the tin plating exists serious phenomenon of alloy exposed. PCB bare board for biopsy can also be found to copper tin alloy, measuring the thickness of approximately 2 (including m, after considering alloy will leads to thickness increases, speculated that the original tin thickness should be below 2 (including m, therefore concluded that the root cause for the thickness of the tin is too thin, Below (including 2 m) That copper tin alloying has been exposed to the welding pad surface, do not have enough tin can again to the solder paste, solder effect, in turn, affect the welding pad. Double spray tin boards ( Circuit board) Single-sided tin bad on how to deal with this should be an article on finishing, gather the opinions of the parties to the article, but when it comes to the end mostly attributed to spray tin thickness is too thin, so that cause bad soldering. Tin thickness suggest at least more than 100 u & # 8221; ( 2. 5µm) More than in the bedding face copper area, 200 u & # 8221; ( 5. 0µm) Above the QFP and peripheral parts, 450 u & # 8221; ( 11. 4µm) Above the BGA welding pad, more can solve the second surface reflow welding from the problems, but the tin thickness is thicker, the more damage it will do fine feet between parts, the problem of short circuit. Process on PCB, the smaller the solder tin thickness will be more thick, easy to fine a feet parts cause a short-circuit. Tin boards ( Circuit board) The longer the storage time, grow in IMC ( Cu6Sn5) Thickness can be jumped over thick, will become bad subsequent reflow soldering. Usually spray the formation of tin plate, the thickness becomes thinner.
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