Improved soldering of components with different thermal masses by hybrid printing of solder pastes
In this work are shown the results of an improved Pin in Paste (PiP) technique. With the purpose of soldering of SMD and PTH (Pinthrough Hole) components, the PiP technique is making use of solder paste printing. The problematic PtP soldering due to thermal shading of areas under large size connectors, which results from their big thermal masses, has been considered. The actual temperatures under such connectors differ from the optimum thermal profile needed for the particular solder paste which profile can be monitored by a KIC instrument. A solution of this problem is suggested by making use of a solder paste, whose optimum thermal profile corresponds to the actual thermal profile under the connector components. For that purpose are used two different kinds of solder pastes. The proposed method, named Hybrid Printing, of two kinds of SMD pastes is based on the special design of a rakel which allows depositing of more than one kind of solder paste within one processing step. The effect of the use of Bi containing, Pb containing and Pb-free solder pastes has been investigated. The application of hybrid printing in a real production line has been demonstrated. The results of the X-ray and metallographic assessment of the fabricated solder joints are presented.
A case study of emission microscopy for ESD protection devices
The paper presents an investigation of a typical ESD protection device with a photon emission microscope. The photon emissions from a normal and failed p-n junction with tunnelling breakdown are compared. The failure is caused by the ESD event. The comparison provides root cause analysis of the ESD failure, recognition of the physical mechanism to enable further analysis of ESD failures in integrated circuits.
Pb-free Assembly, Rework, and Reliability Analysis of IPC Class 2 Assemblies
A team of NEMI companies collaborated for three years to develop Pb-free assembly and rework processes for double-sided, 14-layer, printed circuit boards (PCB) in two thicknesses (0.093" and 0.135") with electrolytic NiAu and immersion Ag surface finishes. This work followed the initial SMT manufacturing feasibility effort carried out by the first NEMI Pb-free development team (1999-2002). All SMT assembly, PTH wave assembly and component rework processes were carried out on production equipment. Various test vehicles including the reliability test board were used in a multiphase development project to develop Pb-free assembly and rework parameters and temperature profiles prior to a 100-board process technology verification build. Following the double-sided SMT and wave assembly build, half of the printed circuits assemblies were passed through a series of representative component rework protocols. Each build group was then subjected to a series of mechanical and thermal reliability stress tests, including 5700 cycles of 0 to 100degC, followed by failure analysis. A special test board was designed utilizing a high temperature laminate designed for Pb-free soldering. Approximately 30% of the assemblies were SnPb control samples. This paper will present the Pb-free SMT assembly and rework development process using the NEMI Sn3.9Ag0.6Cu solder, and results of the reliability stress tests. The rework of large, thick PCB's with Pb-free solder poses a significant challenge to the industry. The lesson's learned and recommendations for future work will be discussed