Reliability of Critical Assemblies When Implementing a New Cleaning

Rich Brooks, James Fugate
Spartronics LLC
Fl, USA

In recent years, there have been significant improvements in soldering and cleaning chemistries, and, in addition, the complexity of the PCB assemblies has also drastically increased. Because of the increase in PCB assembly complexity, the cleanliness of high-reliability assemblies has become more critical for the product’s performance in the field. Therefore, the process and procedure can be very complex and complicated when qualifying a new cleaning chemistry and wash system for these high-reliability assemblies.

Spartronics developed a reliability testing matrix that included multiple soldering materials (e.g., paste, wire, fluxes) and their interactions. The reliability validation testing included the following processes: Label Application, SMT Paste Application, SMT component placement, Solder paste reflow, Wave soldering, Selective wave soldering, Manual soldering, Rework, BGA rework, and In-line cleaning. The following reliability tests were completed: Surface Insulation Resistance (SIR) testing, Ion Chromatography, and ROSE testing.

The reliability testing results concluded that the new cleaning process was in control and provided excellent cleanliness for all the various soldering process interactions. Finally, a comparison of the cleaning chemistries was completed on the effectiveness of component integrity, part markings, silkscreen, and printed labels on real PCB assemblies. These assemblies were washed 12 times through the in-line washer and inspected for any degradation.

This paper will provide the detailed process set up and parameters completed for the experiments and the test results.

Spartronics completed reliability testing that included multiple soldering materials (e.g., paste, wire, fluxes) and their interactions. The matrix included SnPb No Clean, SnPb Water wash, and Pb-free No Clean fluxes, along with every process step: Solder paste printing, reflow, wave soldering, selective soldering, manual soldering, rework soldering, and in-line cleaning. Surface Insulation Resistance (SIR) testing was completed using the Umpire 2 Test boards, and all the flux combinations and variations passed the minimum test requirements. Site-specific Ion Chromatography was completed on the Umpire 2 test boards, and three customer assemblies, and all the ionic residue measurements were lower than the maximum allowable contaminate levels specified by IPC TM-650, 2.3.28.

The new cleaning chemistry and cleaning process passed all the IPC and testing requirements for implementation. Additionally, the new cleaning chemistry was tested for excessive cleaning and effect on labels, component markings, and any other degradation and showed no significant difference from the older chemistry. The new chemistry and process have been implemented and have significantly improved in removing flux residues and eliminating the occurrence of white residues from the circuit assemblies.