In our operation, we currently clean all bare boards before running them through the assembly process. After automated assembly (using RMA based solder paste), the boards are cleaned again in our in-line cleaner or vapor degreaser. The bare boards are also cleaned in either the in-line cleaner or vapor degreaser, both of which are probably over kill. These boards go into military radar systems. My questions are: 1. Most of our boards come in visually clean. Occasionally, we get some boards that look oxidized. What is the risk of not cleaning? *I guess I will dissent from the other responders. Visual cleanliness is seldom useful when you are trying to determine the true cleanliness of the boards. Relying on the IPC-6012 limit of 10 micrograms NaCl/in2 is poor, at best. If you have a board that is consistently 9.5-9.9, you meet the spec, but you still have a contaminated board, in my opinion. When I was at CSL, we did a high volume of determining cleanliness of bare boards. I saw far too many times where the boards met IPC specs, but still had many corrosion and metal migration issues. This was more the case for no-clean assemblers, but occurred occasionally with OA and RMA flux users. This is the risk of not cleaning. *You are basically asking the question, do I need to clean my bare boards? The answer is, It Depends. Ask yourself two questions: (1) how many board suppliers do I have (each of which uses different materials and processes); and (2) how confident am I that ALL my suppliers understand bare board cleanliness and can consistently deliver clean product to me? I did a paper at Nepcon 95 looking at the bare board cleanliness of 6-8 board suppliers to a major automotive assembler in Kokomo, IN (which shall remain nameless, chuckle chuckle). Some suppliers were rock steady all year. Some had occasional blips. Others wouldn't know a clean board if it ran up and bit them. If you are certain that your bare board suppliers understand board cleanliness, and consistently provide you with acceptably clean product for your hardware, then you don't need to clean. But until you can answer those questions, I suggest you keep cleaning. *I will illustrate with two examples (it's my lunch hour and I can type as much as I want): One client had the job of watchdogging bare board cleanliness. He had a horrible time with electrochemical reliability on their hardware. He had 20 board suppliers from all around the globe. Board cleanliness levels all over the map (pun intended). His headaches did not go away until he wittled the list down to about 4-5 and monitored them closely. The second client had a similar situation, but in his low volumes, never had the clout to effect change at his board sources. His company had converted to no-clean assembly, but still had a big aqueous cleaner in the warehouse. In his case, that big cleaner went to the front of his assembly line and all boards entering into the no-clean assembly were cleaned to a known starting point, and his problems (at least the board cleanliness ones) went away. *You have the advantage of still cleaning and using RMA fluxes (or more likely a ROL0 flux, since RMAs don't exist anymore), which are very forgiving of board contamination. The rosin tends to encapsulate board surfaces and your cleaning may address the more aggregious residues on the bare boards. I have found, however, that fabrication residues become progressively harder to remove with successive exposures to reflow temperatures. 2. We're considering a small batch cleaner - something on the order of a Maytag dishwasher with dishwashing detergent. I've seen this used in some small commercial operations. How wide spread is this practice and does it make sense? *I cring just thinking about it. Brian Ellis had some excellent comments. If you go with a commercial dishwasher, they have seals and pumps made for mild detergent solutions intended for dishes (go figure). Those solutions are not what you want on your electronics. Lots of nasty surfactants and most customers don't like their electronics with a fresh pine scent or the smell of lemons. On the other hand, if you put a good saponifier in the unit, one that is good for cleaning electronics and RMA residues, the seals and pumps will only last a few days. I know of one fabricator that regularly rinses their are boards in Cascade detergent as a final clean. Nice shiny solder, nice clean board, loaded with ionic and organic crud. If you are going to clean your bare boards, do it right and not on the cheap. If you would like me to go into more depth, then .......... (here it comes)...... contact me off-line............. (couldn't resist)........ Doug Pauls Rockwell Collins --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------