Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

SIR starting point...?


SIR starting point...? | 21 October, 2002

Is it safe to use the 100M ohm value found in Table 2 of J-STD-004 as a minimum for SIR with respect to flux specification acceptability? It (J4) appears to imply that that value provides some level of acceptability, but it just doesn't come right out and say it. I haven't seen it referenced anywhere else in a standard, but I have heard that spec. referenced before somewhere, maybe here, maybe TechNet.

These are Class 2 boards, not high speed, RF, or high voltage boards, for what it's worth. The specific flux that our supplier wants to use is specified as Class "M" with respect to the copper mirror test, which is another reason I'm getting nervous about this. The bottom line is I don't have any in house specs. to reference, don't have time to develop any, our current flux used in house is much friendlier than the stuff our supplier wants to use.

Yeah, yeah, I know....excuses, excuses..... If this was Class 3, I'd at least know what to say.

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SIR starting point...? | 21 October, 2002

First, SIR data is heavily dependant on the test pattern selected. Be very careful when comparing the results of resistance readings taken from different geometric patterns.

Second, if yer talkin': * Bare boards, yupper. * Finished assemblies imported from China, use IPC 9201 - SIR Test Handbook

For more, look here:

Cool pix of dendrites on page 9.

Another pretty good paper is: Title : PWB CONTAMINATION & RELIABILITY DOE Author : Michael R. Weekes Author Company : Phoenix International Date : 09/30/2001 Conference : SMTA International Abstract : When searching for common industry-accepted test methods to determine the cleanliness of printed wiring boards and assemblies, most manufacturer�s turn to IPC (Association Connecting Electronic Industries) for guidance. It is common to use IPC-A-610 (Acceptability of Electronic Assemblies) as well as IPC TM 650 (Test Methods of Electronic Assemblies) and it�s methods to benchmark the cleanliness or contamination of a process and product. Unfortunately, a chart listing contamination levels for a specific flux and process does not exist.

Contamination can lead to electromigration risk, dendrite growth and subsequent product reliability issues. There are several common, accepted techniques (R.O.S.E. (Resistivity of Solvent Extract)) and modified R.O.S.E. test, SIR test, Ion Chromatography, water-drop-across-trace test, and others). However, there is little consensus as to which test is the best measure of PWB or assembly contamination or cleanliness as well as the test result correlation to long-term reliability.

In the 1980s, prior to the Montreal Protocol and subsequent phase-out of CFCs, manufacturers could rely on CFCs and vapor phase reflow to meet soldering requirements. The eventual move away from RMA fluxes, replacement of vapor phase soldering with reflow and the continual miniaturization of electronics has made the focus on contamination and its link to product reliability more important than ever.

Dozens of pastes, fluxes, and cleaning materials, as well as continued miniaturization of packaging and designs further complicate matters.

This report hopes to achieve several goals: 1. Determine the link between bare PWB contamination, soldered assembly contamination and long-term product reliability. 2. Establish measurable limits for bare PWB cleanliness as well as process control limits for both an aqueous as well as a water-soluble soldering process. 3. Determine whether there is any correlation between common, industry-accepted rose/modified rose (omegameter/ionograph type) testing and long term product reliability. 4. Determine the effect PWB plating finish (HASL, Immersion Silver and Cu OSP) has on both bare PWB contamination as well as soldered assembly in a no clean and water soluble process. 5. Determine whether there is a link between percentage of saponifier used to wash soldered assemblies and long-term reliability. 6. Establish a more cost-effective test for manufacturers to use as a process-monitoring tool.

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SIR starting point...? | 22 October, 2002

After considerable hemming and hawing, we decided to drop the bomb on 'em....give us ORL0 (which we use here) AND no bottom side solder balls or belly up to the bar with some favorable Appendix B test results on their preferred flux.

As usual, Mr. Fish comes up with some more obligatory reading. Cool...somethin' more enlightening than bad copies of solder pot analyses I can't read.

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