Presentation on theme: "Challenges and Solutions for Cleaning No-Clean Flux Residues from Surface Mount Components Eric Camden Foresite, Inc Kokomo, IN."— Presentation transcript:
Challenges and Solutions for Cleaning No-Clean Flux Residues from Surface Mount Components Eric Camden Foresite, Inc Kokomo, IN
Experimental Procedure Test Vehicle Umpire Board Populated with LCC, TQFP, and BGA Other parts available, focusing on low standoff SMT components for this study
DOE Details In this study we looked at four groups of 10 Umpire test boards with identical level of contaminates. 40 Umpire boards were all processed with no-clean paste and then each component area was doped with 5ml of liquid flux, using a syringe to control application. The processing conditions are as follows In this study we looked at four groups of 10 Umpire test boards with identical level of contaminates. 40 Umpire boards were all processed with no-clean paste and then each component area was doped with 5ml of liquid flux, using a syringe to control application. The processing conditions are as follows
Group Details Control – Fluxed Not Cleaned Group 1 – DI water only wash and rinse Group 2 – saponified wash with DI water rinse Group 3 – saponified wash, steam cleaned, DI water rinse
Wash Details 2 FPM 140 o F 60 PSI Top 40 PSI Bottom 52 each 1 GPM Nozzles total for wash, rinse tank mirrors wash.
Test Matrix After the cleaning process all four groups of boards went through SIR testing and Ion Chromatography testing to determine the most effective cleaning approach. All SIR testing was performed to IPC TM-650 188.8.131.52(A), and IC was performed to IPC TM-650 2.3.28, with the IC extractions being performed on localized areas beneath the components after removal.
Control Group Control group was not washed at all after conditioning Examples of BGA, LCC, and QFP on board and underneath components
Control Results Bad. Of course these are worse case scenario type boards but good baseline data for the 3 cleaned groups.
Group 1-IC Results DI water only wash and rinse
Group 1-SIR Results DI water only wash and rinse
Group 1 Results Still Bad. As expected the data after wash with DI water only is better than the control data but still exhibits very high levels of corrosive flux residues, primarily the acetate, WOA, and ammonium. DI water alone does not have enough cleaning energy to remove the uncomplexed flux residues in tight spaces
Group 2 Results Better, but not quite good enough. Group two results; wash with saponifier at 10%, showed much better IC data overall but the WOA levels are still very high and at these levels would pose a mid to high risk of field failures. The SIR data at this level of cleanliness perform better than the first two groups, but still show more failures than not.
Group 3 Results Good! The test results for group 3 show acceptable results on both the ion chromatography and SIR test which indicates good field performance. The steam energy combined with the saponifier on the PCB between the wash and rinse cycles of the in-line process are effective at removing all of the uncomplexed no-clean flux residues.
Conclusions Sometimes more is indeed better. With more cleaning energy applied with steam pushing the saponified wash underneath the low standoff components the results are clear according to ion chromatography and SIR testing, the more energy you throw at it the cleaner and more reliable the product becomes.
Conclusions cont. The parameters in the study are not intended to be implemented into normal production of PCB’s but for rescue and remedial cleaning of contaminated assemblies. Rescue cleaning is becoming a very important option for hardware found to have cleanliness issues long after the boards are built. It is of most importance to remember not to build a recipe according to flux manufacturer spec sheets but to the product being built.
Secondary Study Flux residues are introduced to PCB’s in a number of ways. Hand solder Hand solder Selective solder Selective solder Touch up Touch up Repair and Rework Repair and Rework
Real World Problems A customer came to Foresite with a problem with boards failing at ICT and even more after environmental testing. Most of the process was WS flux and the PCB’s are washed after wave with a few components being hand soldered after wash due to water intolerant issues.
Real World Problems After looking at the entire process all of the thermal profiles were well within acceptability limits on the reflow and wave solder equipment. A large water intolerant thru-hole transformer was being hand soldered after wash. Line operator was using a bottle of liquid flux to achieve better solder joints faster without regard to the effect of non-complexed no-clean flux has on neighboring components.
Real World Problems Transformer has large thermal dissipation properties and required massive amount of heat to fully complex the NC flux, and make an acceptable solder joint. Liquid flux was spreading to resistor network adjacent to transformer without being fully complexed and causing the failures.
Real World Problems Customer did not want to use localized cleaning due to the issues with water intolerant components. Also did not want to use pen type de-fluxer because of the flux being under resistors. Solution?
Real World Solution Send the PCB’s through another thermal excursion to fully complex the flux using a reflow oven. Lose the bottle of liquid flux! Further education for line operators to convey how every action impacts the quality of the boards.
IC Results The PCB’s were tested with ion chromatography to ensure that secondary thermal excursion was effective at complexing the flux
IC Results Looking at the IC results from a localized extraction area over the resistor network before and after thermal excursion the levels of ionics is reduced to an acceptable level.
Final Conclusions Flux is good Active flux after the build process is bad Thermal mass plays an important role in soldering that no flux spec sheet can adjust for. Flux can come from many sources Selective wave Selective wave Palletized wave Palletized wave Secondary hand solder, repair/rework Secondary hand solder, repair/rework Localized cleaning Localized cleaning Bottles of liquid flux are among the worst offenders. Bottles of liquid flux are among the worst offenders.