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18 The PCB Magazine • February 2016 form metallurgical bonds both between them- selves and the exposed copper foil. The second type is referred to as a conductive paste and is comprised of silver-coated copper particles in a binder material which shrinks during cure. These materials and their operation are illus- trated in Figure 4. The second area of application of metal pastes for vias is used in concert with plated- through-hole vias in PCBs. Through-hole vias are vulnerable features when exposed to the high temperatures required for commonly used SAC alloy solders. To protect the vias, via fill ma- terials are often called on to mitigate the strain new Material and proCess solutions for the eleCtroniC interConneCtion industry Figure 5: Tatsuta has formulated different types of materials in the via fill space for different applica- tions. The "non-conductive" copper epoxy paste on the right is designed to manage expansion and protect plated-through-holes. While not suitable for electrical purposes it does have a measure of ther- mal conductivity. The conductive pastes are designed to provide better thermal conduction. Figure 6: The efficacy of Tatsuta's conductive paste AE1244 is demonstrated by the test performed. note that this test was to demonstrate the potential of the material; different designs and components may require a modification to this.