Z. Drozd

A reliability study of the lead-free solder connections of miniature chip components on hybrid circuits

The results of the influence of lead-free solder paste, design and process parameters on the attachment reliability of chip surface-mounted components (SMCs) on thick-film conductor pads are presented. The purpose of the investigation was to compare the quality of the soldered joints made with new solder pastes that do not contain lead with joints soldered with standard SnPb solders. The miniature zero-ohm chip resistors were soldered with selected lead-free solder pastes. The visual appearance of the solder joint according to the standards of lead-free soldered components was compared with components soldered with SnPb solders. On the test sample with soldered chip resistors connected in series, the solder-joint resistance was measured before and after temperature cycling. On the same test sample the solder-joint resistance changes were measured with impedance spectroscopy. After temperature cycling the damaged samples were analysed with SEM and EDS. The reliability test results after temperature cycling indicate two lead-free solder pastes that are the most convenient for chip-component soldering on thick-film conductor pads with the reliability of the joints being equal or better than solder joints with Pb-containing solder paste.

Thermal and Mechanical Reliability Tests of Lead - free soldered SMT Joints

One of the main goals in development of electronics manufacturing technology, after implementation of EU Directive RoHS, is the reliability improvement of electronic interconnection systems. Investigations of lead-free technology for small producers of electronic equipment (SMEs) were made in Warsaw University of Technology (WUT) in frame of GreenRoSE Project financed by EC. Achieved results of accelerated thermal and mechanical cycling fatigue tests of SnPb37 and lead-free SMT solder joints are presented. Two PC test boards finishes: immersion tin and leadfree HASL were applied. The samples were assembled and soldered on GreenRoSE pilot line. Thermal cycling (air to air) tests were performed in two zone thermal shock chamber. For mechanical tests was used new laboratory stand designed by WUT (Szwech and Wrona, 2006). The failures occurred during the tests were detected by four point resistance measurements and visual inspection. The results showed that achieved reliability data of lead -free soldered joints are satisfactory, however, for high reliability applications, further investigations are necessary.

Resistance Measurements of BGA Contacts During Reliability Tests

For mechanical fatigue tests were designed special test models of BGA package and test board, for measurements of solder joints and ball contact resistance by four-point method, with elimination of paths resistance. This solution allows the early and partial failures detection. The mechanical fatigue test was performed on developed mechanical test stand. The resistance was measured before, during and after reliability test. The preliminary results showed that evaluated test method can be applied for accelerated verification of soldering process especially during implementation of lead-free technology.

Quality Management in Electronics Manufacturing after Implementation of RoHS Directive

The improvement of electronic interconnection systems reliability after implementation of EU Directive RoHS is currently one of the main goals in development of electronic equipment assembly. In fact, the reliability of equipment is created mainly during design and production stage. But these phases should be proceeded by research phase. During this phase the ecologically friendly materials and ecologically friendly technologies have to be selected and evaluated. Investigation of Pb-free technology for small producers of electronic equipment (SME s) were made in Warsaw University of Technology (WUT) in frame of GreenRoSE Project financed by EC. First part of our work was concentrated on analyze the influence of reflow oven parameters setup on soldering temperature profile and related with it electrical and mechanical properties of solder joints. On the base of performed experiments the optimal oven parameters were selected and test samples were manufactured. Finally, the reliability data of SAC and SnPb solder on PCBs with Sn and SnCu HASL finishes were investigated and compared.

Mechanical cycling in accelerated life - time tests of lead - free soldered joints

Typical accelerated life-time tests of soldered joints are temperature cycling and thermal shock cycling. In last time other, more economical and effective methods are searched. In Warsaw University of Technology was developed the mechanical cycling method and appropriate test stand. The test samples of printed circuits with soldered components are bent with constant radius at all length of the printed circuit. The new method seems to be perspective, especially for small producers of electronic equipment, because of low costs and short test time. FEM analysis and first tests showed that new method can be useful, especially by testing of lead-free technology, implemented according to ROHS Directive of European Community

Infant mortality failures of lead — free solder joints

Two goals of the work - verification of suitability of mechanical tests of solder joints reliability and infant mortality (early failures) of lead-free joints are selected. The results of reliability tests of lead — free solder joints of SMT resistors showed a tendency to increase of infant mortality failure rate comparing to SnPb eutectic joints. These new results are presented. Soldering process parameters, manufacturing equipment, testing methodology and working conditions of lead — free electronic products are discussed and compared to SnPb solder joints technology. Infant mortality and fatigue caused cracks after thermal and mechanical tests are shown in photos and metallographic sections. Statistical results are presented in Weibull plots and failure rate characteristics. Achieved results of primary failures data are presented and discussed. Practical conclusions for manufacturing technology are specified.

Life-time of lead-free soldered SMT joints

The work concern the life-time of electronic products according to ROHS Directive of European Community. Methods and results of accelerated mechanical and thermal cycling fatigue tests of SnPb and lead-free solder joints, realized in GreenRoSE EC Project are described. The aim of the work is development of cheap test methods, applicable by small producers of electronic equipment. Thermal shock cycling method and mechanical method of cycling bending of PCB samples with soldered SMT and BGA components were applied. The investigations showed the possibility of simplified reliability assessment of lead-free electronic products by mechanical fatigue testing. Advantage of this method is lower cost and shorter test time as by thermal cycling. The planes of further research for obtaining more detailed data are discussed.

Assembly Problems in Lead-free and Mix Production

Some electronic assemblers are faced to face with the necessity to use heterogeneous assembly of both very large and very small components on the same board and mix tin-lead and lead free soldering technology. Authors try to solve the problems with pick and place very small components by special design of stencil and adjust printing and assembly parameters. The solution of the soldering problems they try to solve by optimization the soldering profiles for mix technology.

Economic reliability test methods of new soldering materials

According to RoHS directive, many new electronic products are manufactured by using of new technology and lead – free soldering materials. For reduction of the risks concerning quality and reliability of such products are necessary accurate investigations. Reliability tests of electronic interconnections are time consuming and expensive. In Reliability Laboratory of Warsaw University of Technology (WUT) are studied different test methods and optimal method, applicable by small producers of electronic equipment, is searched. In this paper are presented last results of mechanical shearing test method and compared with applied before [1] thermal cycling and mechanical flexion methods. The application area of each method is discussed. These results show that the test time and costs can be drastically reduced by application of mechanical methods. The goal of performed research is preparation of the proposal for standardization.

Influence of PCBs coatings wettability on lead-free SMT solder joints reliability

The paper presents results of wettability study of PCBs with immersion Sn, Ni/Au and SnCu coatings before reflow soldering process. Furthermore the solder joints were made in the optimal lead-free reflow soldering conditions using chosen materials with different wettability value of PCBs coatings and their reliability assessment was executed. The results of investigations have shown that exist direct influence PCBs coatings wettability on reliability of solder joints. It was find also that by using special procedure of PCBs coatings wettability assessment it is possible to predict future solder joints reliability.