Werner, Given the broad array of assemblies being constructed today, both in terms of size and in terms of types/density of components, how can you ever know how inaccurate your measurements are unless you use a fully populated board. For some designs, a bare board with few components may be completely acceptable. But for others, it may lead to significant errors. Jeff Perkins -----Original Message----- From: Werner Engelmaier [SMTP:[log in to unmask]] Sent: Thursday, November 12, 1998 8:29 AM To: [log in to unmask] Subject: Re: [TN] Temp Profiling Hi Tom, In a message dated 11/11/98 18:14:10, you wrote: >Werner, >Perhaps I should clarify my question. My question is if temp >measurements using bare fab and few components on it including the >biggest thermal mass and few passives are inaccurate, should I use the >first loaded board prior to reflow?(just out of the PnP) and if so, >should I place the thermalcouples in the solder paste or on the lead? >Tom Han >Ardent Systems You make an assumption, that "temp measurements using bare fab and few components on it including the biggest thermal mass and few passives are inaccurate." I do not agree with this premise, unless you have an old reflow machine. Modern so-called 'Convection'-machines, and even the late generation so-called 'IR'-machines (I put the emphasis 'so-called' on them, because these nomers are conventions and do not describe the complete heat transfer situation), have sufficient heat transfer from both IR and covection, that neighboring components have no significant impact on each other. Since the leads are the slowest heating parts of the solder joints, it is best to place the thermocouples on the leads. Make sure, that the thermocouples are placed so not to interfere with the heat transfer to that solder joint; and use the thinnest thermocouple wire you can handle to avoid errors from the thermocouple wire. Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask] ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################