In a message dated 06/15/2000 5:20:22 PM Central Daylight Time, [log in to unmask] writes: > Bev > > Please follow your own suggestions and check the TechNet > archived. I talked about this several months ago. I have used the term " > Immersion White Tin" since 1995 to describe a coating called OMIKRON. I took > the name from an IBM research paper published back in 1984. They used that > term to describe a long term solderable immersion tin finish. It has > nothing to do with your definition. > > Rich Edgar Hi Rich! The "White Tin" in the term "Immersion White Tin" is what sometimes confuses many people. Bev described exactly what "white tin" is from the periodic table of elements. So you are right, his description of "White Tin" has nothing to do with OMIKRON, just as the words "White Tin" in "Immersion White Tin" has nothing to do with the actual description of White Tin in the periodic table of elements. Bev is probably more knowledgable in material sciences than many people, that's why he has his PHD. Not to speak for him, but I'd bet he was talking about white tin as it's clearly defined from the periodic table...not from your "trade name"... There's some pastes below from a few web pages that talk about white tin, organic tin, white immersion tin...whatever you want to call it. This ought to confuse everybody :) -Steve Gregory- From: http://pearl1.lanl.gov/periodic/elements/50.html Properties Ordinary tin is composed of nine stable isotopes; 18 unstable isotopes are also known. Ordinary tin is a silver-white metal, is malleable, somewhat ductile, and has a highly crystalline structure. Due to the breaking of these crystals, a "tin cry" is heard when a bar is bent. Forms The element has two allotropic forms at normal pressure. On warming, gray, or alpha tin, with a cubic structure, changes at 13.2 degrees C into white, or beta tin, the ordinary form of the metal. White tin has a tetragonal structure. When tin is cooled below 13.2 degrees C, it changes slowly from white to gray. This change is affected by impurities such as aluminum and zinc, and can be prevented by small additions of antimony or bismuth. This change from the alpha to beta form is called the tin pest. There are few if any uses for gray tin. Tin takes a high polish and is used to coat other metals to prevent corrosion or other chemical action. Such tin plate over steel is used in the so-called tin can for preserving food. Alloys of tin are very important. Soft solder, type metal, fusible metal, pewter, bronze, bell metal, Babbitt metal, White metal, die casting alloy, and phosphor bronze are some of the important alloys using tin. Tin resists distilled sea and soft tap water, but is attacked by strong acids, alkalis, and acid salts.Oxygen in solution accelerates the attack. When heated in air, tin forms Sn2, which is feebly acid, forming stannate salts with basic oxides. The most important salt is the chloride, which is used as a reducing agent and as a mordant in calico printing. Tin salts sprayed onto glass are used to produce electrically conductive coatings. These have been used for panel lighting and for frost-free windshields. Most window glass is now made by floating molten glass on molten tin (float glass) to produce a flat surface (Pilkington process). Of recent interest is a crystalline tin-niobium alloy that is superconductive at very low temperatures. This promises to be important in the construction of superconductive magnets that generate enormous field strengths but use practically no power. Such magnets, made of tin-niobium wire, weigh but a few pounds and produce magnetic fields that, when started with a small battery, are comparable to that of a 100 ton electromagnet operated continuously with a large power supply. From: http://www.omnigraph.com/omnireview.html Organic White Tin About six months ago we sent out samples of white tin finish on printed circuit boards. Some people liked it and some did not. Those that did not like it had solderability issues. It didn't wet as well as Hasl. We had difficulty in figuering out why it did not wet as well. Was there a difference when the assembler used a water soluable or no-clean flux? Did the soldering temperture make a difference? It turns out the biggest problem was the plating thickness in our process. We thought if it looks good then it should work. We discovered that .2 microns of white tin look good but there will be de-wetting. And .4 microns wets fine for a single thermal pass, but will cause difficulty on subsequent thermal passes. For multiple thermal passes, .6 to .8 microns of plating is required. We have decided to be on the safe side and plate .8 to 1 microns on all our boards. To refresh your memory, here are some characteristics of white tin. THE HASL REPLACEMENT IMPROVED IMMERSION WHITE TIN Compatible with all fluxes and solder pastes Capable of multiple assembly cycles Uniform flat and dense pads Shelf life equal to hasl No solder pot contaminaton Can be electrically tested after coating This coating will not add cost to your board and will guarantee your product acceptability in the Japanese and European market in 2002 and thereafter. We will be sending more samples out to you for testing. Please try this process again. From: http://www.filtranmicro.com/desgui.html B) White Immersion Tin Filtran provides immersion tin processing using Omikron chemistry. Typical thickness will be under 40 microinches (1 micron). This finish is thin and will not affect the circuit resolution as will 300-500 microinches of tin-lead solder. Immersion tin acts as an acceptable solderable coating with a shelf life of 6 - 12 months if stored under ideal conditions. Tarnishing can occur when exposed to moderately hostile environments. In such cases, a mild acid cleaning and/or light abrasive cleaning immediately prior to soldering is recommended. ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################