~clapping~ Okay I am impressed. It never fails though, every time I offer a little advice, one of you comes along and just blows my miniscule offering clean out of the water. But then, it never hurts to be humbled. Thanks for the info, hope it's not copyrighted, 'cause I'm cut'n and past'n right now. Franklin -----Original Message----- From: Sherry Goodell <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Date: 07 October, 1999 4:31 PM Subject: Re: [TN] HASL-contaminated solder pot Julie, Soldering processes, by nature, are considered complicated and involved due to the various factors that must be maintained and monitored. Most of these factors are indigenous to the process, such as pot temperature, dwell times, and contamination levels. Items such as temperature and dwell times are readily measured, adjusted, and understood, making them some of the more comfortable aspects of the soldering process. Solder contamination, on the other hand, tends to be a less understood phenomenon. To accurately determine trace contamination levels in solder requires very specific analytical equipment and precise analytical methods. I agree with Franklin, You need to collect data and establidh the trends for your production. In our solder service we send out a sample daily to ensure compliance. In a board shop you can reduce that considerably after you establish how many surface square feet you are processing and the the rate at which the copper is rising. Most solder suppliers provide multielement analysis beyond tin, lead, and copper. Once levels of contaminants have been determined, interpretation of these results may require assistance based on your particular problem. Your solder supplier should be able to assist you. Typically, copper contamination and tin concentration are targeted as the gauges of the relative health of a solder bath. The introduction of gold is also a critical contaminant requires watching. Copper, being the most typical contaminant, is probably the best understood in soldering circles. Manifesting itself as an intermetallic along with tin, it is necessary to deal with it. A normal by-product of the formation of the solder bond on the board surface, it migrates outward from the board into the solder pot, where it typically becomes soluble and homogeneous. There are two forms of this material, Cu3Sn and CusSn6, of which the latter is more prevalent. There will come a point in the lifetime of any solder bath where the solubility of the copper/tin intermetallic will be at or near the saturation point. Boards processed under these conditions [approximately 0.30 percent by weight at 470° F (243° C)] will show a pronounced gritty appearance. The reason for this is that the intermetallic, being less dense than molten tin/lead, will migrate to the top of the deposit where the characteristic dendritic crystalline structure will create the gritty surface. This poses a problem, both in terms of esthetics and in solderability. The presence of a concentrated copper in the relatively small volume of solder located on a pad will raise the thermal demand requirement on a local level, compromising the reflow characteristics of the solder deposit. Gold is another typical contaminant of a solder bath if it is being used to process boards that have been previously tab plated. AuSn4 is another intermetallic that will form if solder is allowed to contact gold-plated surfaces. Utmost caution must be taken to avoid this occurrence, because gold is approximately six times more soluble than copper and can be even more detrimental to the solder joint. Gold contamination will be visible as a frostiness of the solder deposit with an accompanying embrittlement of the solder joint. A joint produced under these conditions can be prone to failure under thermal cycling or high vibration environments. Adequate protection of the gold from solder contact or elimination of pre-gold plating are the keys to controlling gold contamination. It can not be removed by any user-available methods--only by sophisticated metal treatment systems or solder bath replacement. Variation of tin concentration can have a pronounced effect on solder performance, but there is a reasonable window in which to operate that is not difficult to maintain. Typically, most processes will run well between 61.5 and 63.5 percent tin concentrations. The danger in running above or below this range is the change in melting points and subsequent variation in surface tension characteristics. Surface mount processing poses particular problems primarily in that surfaces devoid of a hole demonstrate low surface-energy characteristics. As such, they resist the efforts of fluxes and solder to achieve lower free-energy states and wet the copper surface. Sufficient deviation from the eutectic alloy ratio can affect later reflow performance in high-speed, low-temperature soldering applications. An important factor to consider when examining the soldering of a board or a given area is that, although a pot might exceed the melting point of the solder deposit, there is a heat sink effect of the board and flux that will lower the overall amount of energy transferred to the board, decreasing the ability to melt the solder deposit. The physical scale we are dealing with in terms of thermodynamics is small enough to deviate from what we would consider correct and to force us to reevaluate our way of troubleshooting and investigating problems. Contamination levels that are unknown can play a huge role in the repeatability of the process. Julie, if I can be any more help please contact me off line and I can get you some additional information. Good luck Sherry phone: 603-437-8653 Fax: 603-43404156 e-mail: [log in to unmask] or [log in to unmask] > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Julie Dixon > Sent: Thursday, October 07, 1999 2:59 PM > To: [log in to unmask] > Subject: [TN] HASL-contaminated solder pot > > > TechNet, > > We have sporadic problems with the copper level rising in our > solder pot. We > reduce the temp and dross each morning. Could you recommend a specific PM > program to keep our SnPb clean? We believe per the certicates of analyses > that > our supplier gives us good product. Any other reasons it might rise? > > Thanks, > Green > > ############################################################## > 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 Gayatri Sardeshpande at [log in to unmask] or > 847-509-9700 ext.5365 > ############################################################## > ############################################################## 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 Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################