Mel- Thanks for the info! Yes, I can certainly see that the meniscus would prohibit wetting. And, especially, in the worst of all situations - meniscus in the solder joint when in a single sided board application - the premature failure over time and temperature extremes seems quite likely. What I'm also concerned about, though, - and this is the predominate debate point, here - involves potentially compromised PTH's, when the meniscus in the holes is allowed. Won't the partial blockage of the hole create a potential entrapment of flux gases or residues? And, if that is so, it seems like at least two problems may result: 1 ) a diminished area of wetting inside the PTH (and therefore a weaker mechanical junction of less current carrying capability) and 2) the potential for a breakdown of that hole plating due to either corrosion or expansion and contraction of the trapped materials (or would it be due to the relative differences in TCEs of the plated hole and the trapped materials?). A third possiblity might include the breakdown due to increased heat generated at these highly resistive pockets. I know it sounds like I'm answering my own question, but I haven't seen any reports or articles that back me up. I'm questioning my own paranoia, I guess. Y'see, if those points are valid, then the justification for the spacing is self-evident. If not, well....Good! I can relax a little. So, am I out to lunch on this or what? Lunch? Oops, gotta go. Thanks, again! ---------- From: MTTC To: internet!ipc.org!TechNet-d; JMcgee Subject: Re: MeniscusBlockage Date: Wednesday, November 13, 1996 9:48AM John, It is true that the requirements have changed from J-STD-OO1A to B for meniscus in the solder connection. IPC-A-610B was compatible with the J-STD-001A. The condition was downgraded to "should" which is a recommendation (para 1-4, 001B). We should also consider that there still remain some wetting requirements for the solder connection in the B revision. Since solder cannot adhere to meniscus, the wetting characteristics of the connection are affected. The failure mechanism reflects the fact that solder cannot wet to component meniscus material. Severe environments could cause the resulting solder joint to fail. Another consideration was damage to the component, which I cannot see except in extreme cases. Personally, I have seen many solder connection failures resulting from this condition during service life of products (including class 1 and 2). The condition becomes doubly critical when single sided boards are employed due to minimal solder strength and intrusion of the meniscus through the PWB. I don't know of any test reports regarding the condition. If they were available, it would have been from the Mil Spec world to justify the Military Standard content and since they traditionally required consideration or corrective action it became a mute point through years. Best regards Mel Parrish President, MTTC Inc. On Tue, 12 Nov 1996 10:54:00 +0000 John McGee wrote: "Looking for clarifications, please...In J-STD-001A, Section 6.6.4.5 -'Meniscus Spacing &Trimming' it was stated that '...Components SHALL be mounted to provide a visible clearance between the coating meniscus (on each lead) and the solder connection', making it mandatory for Class 3; If products in Classes 1 & 2 did not meet the process control requirements, this condition was mandatory, too. Otherwise, it was a Recommended condition for Class 1 or 2. In my pre-release copy of J-STD-001B, the statement reads ' ... Components SHOULD be mounted...' in that way. I see no interpretation of the word 'should' in section 1.4 and , as well, no differentiation among the Classes. 1) Is the interpretation cleared up in the released version of -001B? 2) Has the requirement really changed since the previous revision? In IPC-A-610B, Section 3.2.4- 'Component Installation-Vertical - Radial Leaded' and 4.2.3- 'Soldering-Meniscus in Solder', the 'clearance-required' condition is illustrated. It's clearly shown that meniscus in the PTH is unacceptable for Class 3 assemblies. With certain provisos, however, meniscus in the holes is acceptable for Classes 1 & 2. As a Class 2 house (for now), wary of unnecessary costs- such as those associated with spacers or special lead forming- we periodically debate the intent of this requirement. 3)The clearance requirement is for more than just inspectability, isn't it? 4) What aspect of reliability is potentially compromised when the meniscus isallowed in the holes? 5) And in what ways will this breakdown manifest itself? 6) Where may I find technical papers or test data that will help to illustrate this condition?" We can be reached at: e-mail: [log in to unmask] Manufacturing Technology Training Center (MTTC), Inc 543 Graaf Street Phone 619 446-5571 Ridgecrest CA 93555 Fax 619 446-4337 Home Page: http://www1.ridgecrest.ca.us/~mttc/mttc.htm Bulletin Board: 619 446-4087 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************