Impact of No-clean Fluxes Cleaning on PCB Ionic Contamination Karel Rendl, Václav Wirth and František Steiner University of West Bohemia/ Faculty of Electrical Engineering/ Department of Technologies and Measurement, Pilsen, Czech Republic krendl@ket.zcu.cz Abstract: The paper describes the dependence of the ionic contamination of PCB after the soldering process with no-clean solder pastes on the type of cleaning. For the experiment three different types of solder paste were selected. Solder pastes were labeled as no-clean. The samples were reflowed with two different soldered profiles. The ionic contamination after soldering process was measured. Contamination of PCB was investigated to set up of solder profile. Then three different types of rinses were applied to the samples. The rinsing medium was deionized water, 50% deionized water with 50% isopropyl alcohol (IPA) and IPA. The cleaning process was set to 10 minutes in an ultrasonic cleaning bath. Then rate of ionic contamination after application of cleaning the PCB were monitored. From the results there were determined by a recommendation on whether it is necessary to clean no-clean solder paste. 1. INTRODUCTION Solder pastes are an integral part of the process of reflow soldering. These pastes contain balls of solder alloy and flux. The flux removes oxides from soldered surfaces and helps to improve solderability [1]. The residues of fluxes may cause a variety of defects after the soldering process. Therefore, the soldering process is usually finished by the cleaning process. The cleaning process is costly and the whole production process is prolonged. Until year 1987, 98 % of PCBs were cleaned after soldering. Then the no-clean technologies were applied into production and cleaning process wasn't used (80 % of PCBs wasn't cleaned after soldering). At the present, producers of PCB are returned to apply cleaning process (53 % of PCBs with no-clean fluxes are cleaned). Some PCB producers recommended cleaning no-clean technologies, that they prevent defects on PCB. Other producers don’t recommend these technologies cleaning from reason more expensive process. From these reasons it is necessary deal with questions of cleaning and ionic impurities of PCB. The conformal coating is often applied on the PCB and therefore PCB must be sufficiently pure. For this reason it is also necessary to deal with the ionic purity [2]. The implementation of lead-free solder alloys changed soldering process. The melting point of these alloys is higher than the melting point of lead alloys. It is necessary to use a more activated flux to remove oxide layers from the soldered parts. These soldering fluxes leave more aggressive residues. These residues under the action of humidity can cause a variety of defects on PCB. The most critical defects are corrosive and conductive dendrites on the PCB [3]. It is necessary to take measures to prevent defects. Therefore, it is necessary to use a cleaning process or use no-clean technology. Nowadays miniaturization of devices means higher requirements on the PCB ionic contamination and surface insulation resistance. Therefore, it is important to clarify whether it is necessary no-clean solder paste and flux to remove after the soldering process. Whether the ionic impurity of no-clean solder pastes cannot be released on the PCB and cause some defects. IPC standard determine the higher allowed value of ionic impurities of PCB 1.56 µg NaCl/cm 2 . This value was determined some decades ago. Production of electronic devices is different since these years. Insulation gaps are smaller between conductive layers. Therefore it is question whether value of ionic impurities is actually [5].