Hi, all! Please let me set the record straight. 1) Hot oil reflow is NOT the same as hot-oil levelling 2) Hot oil reflow consists of reflowing an electrolytic tin/lead plating, typically about 30 um thickness. It melts the plated metals into solder and leaves a good, thick solder coat, just like IR reflow, except smoother and shinier. The process was usually a three bath affair with simple immersion in oil at, say, 140°C preheat for 10 secs, 230°C fusion for about 3 seconds (more for thick boards) and 190°C quench for a couple of seconds, so that the solder "froze" very rapidly on extraction. 3) Hot oil levelling (such as the Hydrosqueegee) consists of wave soldering or dip soldering the bare board and then removing the excess solder by jets of hot oil. This is the process that, badly adjusted, just left the intermetallics but, correctly adjusted, gave a result quite similar to HASL, except that the coating was slightly more uniform because the interface between the surface tension of two liquids is better than between the molten solder and air, which tends to form a bumpier meniscus. 4) In both cases, 3 types of oil were used. The initial one was Shell Peblum A, which was a mineral oil designed originally for levelling the tin on sheet steel used for making tin cans. For reasons of a) a relatively short lifetime b) a fairly high cost, some intrepid adventurers replaced it with peanut oil. Then some of the flux manufacturers brought out special water-soluble "oils", such as Lonco Fusecote 240. These were, in fact, blends of polyglycols and glycol ethers. They had a lifetime in the machine of about 3 - 4 times that of the mineral Peblum oil at about the same price and much reduced operating costs (water clean, instead of solvent cleaning was also cheaper). 5) All three oils were smelly, unless good ventilation and quite messy, which was their downfall, in both processes. There was also worry about loss of SIR with the water-soluble oils, although this was more worry than fact. They also fell into some disrepute by a number of fires, especially with peanut oil which has a flash point under the melting point of solder. I don't believe there was a fire with the water-soluble oils which had a TAG CC flash point of about 260°C, dropping to about 250°C after about three weeks of 1 shift use. 6) Hot-oil reflow was more popular than levelling as it was a very simple process which was exceedingly easy to control and the fusion temperature, unlike IR, was asymptotic. It was also popular for 3D flex circuits which were simply impossible to reflow with IR. For the anecdote, something like the Hydrosqueegee, but more powerful, is coming back into the thinking within Europe in preparation for WEEE. By putting in an end-of-life assembled board, all the solder can be "washed" off and recovered for recycling. Roughly 95% of the lead and 85% of the tin can be recovered (more tin remains on the intermetallic residues). Hope this trip down 30 years of memory lane will explain. Brian Genny Gibbard wrote: > > You learn something new (or new to you) every day. > I was just told of a board finishing process called Hot Oil Solder > Levelling. It was portrayed as a very flat, nice finish. I was also told > that it is old technology, which may be why I am not familiar with it. It > is only within the last year that I have really gotten involved with > specifying board finishes. I've been searching on the internet to learn > more and am a bit confused. > My questions: > Is Hot Oil Reflow and Hot Oil Surface Levelling the same thing? If not, > what is the difference? > What are advantages/disadvantages to this over HASL, or any of the newer > so-called 'flat' finishes needed for fine pitch? > > Thanks. > > Genny Gibbard (mailto:[log in to unmask]) > > --------------------------------------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------