Dear Andy, Many thanks for your reply. You are exactly correct that we are using no-clean solder paste. It is Heraeus K180. I'm still figuring out a way to remove the resistor without destroying the evidence (dendrites, if any). Any ideas would be appreciated. Regards KK Chin Artesyn Technologies 47173 Benicia Street, Fremont, CA 94538 Andy Mackie <[log in to unmask]> on 02/08/99 01:38:35 PM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to [log in to unmask] To: [log in to unmask] cc: (bcc: KK Chin) Subject: Re: [TN] Voltage Across 1206 SMD KK: There's a myriad of possibilities here, and I'm sure the electronics engineers will have some thoughts on what is happening with the component. I'm assuming that you're using a no-clean flux....Electrical problems with solder paste flux are not very frequent, but if there are signs of electromigration (dendrites), under the components, or haziness or discoloration, flux residue issues are usually indicated. The solvents used in solder paste fluxes are usually assumed to be driven off during reflow, but may remain entrapped if either a./ the reflow profile spike is too low in temperature, or b./ the residues have a significantly reduced surface area (such as when they are trapped under BGA's or other components). Although the solvents used in no-clean fluxes are usually non-hygroscopic (that is, they don't pick up moisture), some are problematical, if they are not volatilized suring the reflow process. If you have a 'capillary ball' which touches one of the component terminations, this will increase the voltage field gradient by reducing the gap, and this can be another factor causing electrical difficulties. I hope this helps. Andy KK Chin <[log in to unmask]> on 02/08/99 03:29:54 PM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to KK Chin <[log in to unmask]> To: [log in to unmask] cc: (bcc: Andy Mackie) Subject: [TN] Voltage Across 1206 SMD Dear Technetters, We see some failures in one of our products due to resistance drop across a 1206 resistor on a PWB assembly. The products failed after hours of operation in the burn-in environment and is suspected to be the effects of SIR drop or electromigration. There's 135Vdc across the resistor during operation. The designer thought it's ok because the resistor itself has a max. operating voltage of 200Vdc. The land pattern is of the IPC-SM-782 standard (1.2mm gap in between). The solderpaste is also claimed to be compliant with IPC-SF-818 and Bellcore TR-78 in terms of SIR and EM. My understand is that SIR and EM are tested with bias voltage of 50Vdc and 10Vdc respectively. Are these standard tests really applicable to this high voltage case? Thanks! KK Chin Artesyn Technologies 47173 Benicia Street, Fremont, CA 94538 ################################################################ 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 ################################################################ ################################################################ 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 ################################################################