Mr Lao We have some specialist knowledge on this subject and offer both equipment and services for these tests. My first recommendation is that take coupons manufactured by your PC Fabricator and then samples at each manufacturing stage: Bare coupon Coupon plus solder resist Solder resist plus flux and or paste, no components with soldering Then same with components over test patterns Ten before and after cleaning, if applicable and before and after conformal coating, if applicable. This should represent some 30 to 40 coupons. The testing MUST be done based upon the same process materials you will use in your manufacturing process so that you can see the actual anticipated synegistic influences of the different process stages and test for product reliability. The SIR testing needs to be done using very frequent monitoring, say 10 minute intervals so that you do not miss any dendtrites formations causing reliability problems. The SIR tester should be equipped with current limiting resistors to protect and preserve these dendrites for subsequent analysis using IC or SEM. I attach some literature in JPEG format for your consderation. Let me know if you have problems reading and I will find another way of sending to you. Maybe you could let me have your mailing address? Regards, Graham.Naisbitt@concoat.co.uk Auto-SIR�, from Concoat Validation of your process The Auto-SIR� system allows the surface leakage currents across representative assemblies to be automatically and accurately monitored whilst they are exposed to high humidity and temperature ageing conditions. Any contaminants introduced onto the assembly by the production process, whether ionic or non-ionic, will be detected in terms of their effect upon the Surface Insulation Resistance (SIR) as the samples absorb moisture and age in testing. Synergistic effects are also detected, providing the essential element missing if manufacturer SIR data for individual products is relied upon. Low SIR values highlight potential reliability issues in the future, before your product goes into full production. The Auto-SIR� can also be used to gain SIR data for individual product validation such as flux. The test requires a comb pattern (interleaved tracks) either on a test coupon or somewhere on your production unit, across which a bias is applied. Often the test coupon will have over-mounted components to provide a more realistic model for contamination entrapment and cleaning challenge. Leakage currents as low as 10-12A are detected across the tracks of the comb whilst the test areas is exposed to high temperature and humidity ageing conditions. Contaminants, which are detrimental to long term circuit reliability, will cause a drop in the surface insulation between the tracks of the comb pattern and will be detected by SIR testing. Due to the high frequency automatic monitoring of the Auto-SIR� unit even dendrite faults which can �burn out� rapidly are detected (not so with manual monitoring). Windows Software - Versatility Windows95 (or 3.1) based software allows almost unlimited flexibility in SIR testing with all readings logged automatically, and all data displayed in a user friendly graphical form visually updated as it is collected. Due to the high frequency of sampling feasible with the Auto-SIR� trend analysis is possible, revealing information about contamination, and dendrite growth as the test progresses. Remember, without high frequency measurements valuable data, including dendritic growth, may never be detected. Two methods for presentation of results can be viewed at anytime during or after testing. The last SIR resistance taken for each channel is shown on a bar chart as the results are logged. This provides the user with a �snap shot� of the test in progress. Any channel can also be viewed individually as it is logged and its progress monitored providing a detailed graph of how the SIR of that channel has behaved over the test period. Totally user definable test parameters including; test duration sampling rate reverse or non-reverse bias bias level 50, 100 or external independent selection and labelling of 128 test channel Standard or user definable labels and full flexibility for choice of channels to be used. Specification templates (e.g. Bellcore, IPC 650 etc.) are built into the software. Selecting will allow sampling rate, number of test channels, and bias used to be pre-loaded. The user can design new test specification templates giving total flexibility to the bias level and timings of every reading to be taken. E.g. take values at 0min, 5min, 30min, 24hrs, 5 days. Process Validation Test Service As well as the equipment itself Concoat are able bring you the benefit of their experience providing Process Characterisation/Validation tests using new Auto-SIR� test methods with Frequent Monitoring, Trend Analysis (FMTA) techniques. SIR testing measures the actual effects of contamination, whether ionic or non-ionic, on the surface insulation resistance of your representative assembly under conditions of accelerated ageing, to better predict the reliability of your product. The testing will be conducted according to J-STD-001B Class 2 or Class 3. It requires special test coupons incorporating interleaved comb patterns that should be processed simultaneously with the customer�s existing production process. The test is for those who wish to obtain a SIR overview of their total process. The coupons must be prepared by production means and entered into the test at subsequent stages of the production process so potential problems can be more readily isolated. The test can be tailored to the needs of the customer, for example allowing them to focus on specific problem areas such a choice of flux or cleaning process. For example, and based upon an original enquiry; Stage 1 Bare FR4 as from supplier 4 coupons Stage 2 Solder resist applied and cured 4 coupons Stage 3 Application of SMT adhesive side 1 4 coupons Stage 4 Application of Paste, reflow 4 coupons Stage 5 Application of flux and wave soldered 4 coupons Stage 6 Application of Paste, components mounted, reflow 4 coupons Stage 7 Application of flux, components mounted, wave 4 coupons If applicable, then: Stage 8 Boards are cleaned 2 coupons Stage 9 Conformal Coating applied and cured 2 coupons Obviously, the manufacturing process and therefore the number of test coupons involved will vary from customer to customer. If only a fully assembled final sample is tested, then any process problems cannot be so easily identified. We consider that, because of the low current test capability, reverse bias is unnecessary, as it does not properly reflect actual assembly operating conditions. From this testing, the synergistic effect of each process step can be seen in the final evaluation. For example low SIR might come from a problem in the bulk FR4 in Stage 1, or may be introduced by a contaminated cleaning tank in Stage 8. Concoat Ltd Alasan House, Albany Park, Camberley, Surrey GU15 2PL Tel: +44 (0)1276 691100 Fax: +44 (0)1276 691227 E-mail: alan.brewin@concoat.co.uk Application Engineers in Chemical Compounds to the Electronics Industry For a quotation please contact Concoat�s R&D Manager, Mr Alan Brewin.
| I'm in the process of running a no-clean paste evaluation. I'm presently writing the | specifications for the laboratory test requirements (SIR testing, flux testing, etc.). | So far, I've developed a very comprehensive set of test criteria using much of the | available standards (Bellcore , IPC, J-STD). However, due to testing constraints which | specific tests are considered as necessary for a basic paste evaluation? For instance, | should an Ion Chromotography or Thermogravimetric test be performed? I would | rather spend the bulk of my time evaluating the production capabilities of a paste and | just send out for the basic necessary lab requirements. Thanks.
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I'm in the process of running a no-clean paste evaluation....
- Feb 13, 1998
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