SMT007 Magazine

SMT007-July2021

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44 SMT007 MAGAZINE I JULY 2021 example of the intended end-product, fully assembled. e examination is to determine electrochemical compatibility between solder mask/resist, solder flux, paste or wire, under- fills, adhesives, staking compounds cleaning processes, conformal coatings, etc. e test standard employs the IPC B-52 that has been evolved from the original research carried out by the NPL. Copies of the NPL research papers have been uploaded to the IPC Works 5-32b website with a free download. e IPC B52 coupon, also known as the IEC TB57, was developed using a selection of dummy components that repre- sent "worst case" process residue entrapment sites. is is not a test that we would recommend for process qualification. It would be an impos- sible task to include a full complement of the components in use today, as much because they must be true dummy components with no internal dies or connections. We are oen asked, "Can SIR testing can be used as a process control tool?" and, "Can it be run for less than 168 hours?" As a major equip- ment vendor of SIR test instruments that trace its origins back to the mid-1970s, GEN3 is very much in favour of this idea. However, and in specific regard to high-vol- ume/low-mix manufacturers, it is unrealistic. SIR testing is neither fast nor simple, and we have too many instances of failures by custom- ers not respecting the many and varied "pro- cedures" that need to be catered for. Equally, WIP (work in progress) will mostly prohibit such an approach. In addition, many no-clean fluxes today exhibit ECM failure beyond 500 hours in ser- vice. is suggests that the test duration pres- ently called out in IEC 61189-5-502 and IPC 9202, might need to be extended from 168 hours to 500 or even 1,000 hours. To achieve acceptable "objective evidence," SIR is recognised by the IPC as the primary technique. It (SIR) doesn't care what is pres- ent that might be causing a failure, it is simply an examination of whether the representative sample (IPC B-52 or other) exhibits accept- able electro-chemical reliability data, irrespec- tive of being ionic or non-ionic. Figure 1: SIR testing.

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