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Für industrielle Lötprozesse in der Elektronikfertigung ist es nötig, die kritischen Parameter zu charakterisieren, die zum Erzielen von optimalen Lötstellen nötig sind. In dieser Studie durchlief ein Baugruppentyp sowohl eine Wellen- als auch eine Selektivlötanlage. Frühere Studien, in denen man Ergebnisse dieser Lötanlagen verglich, zeigten, dass sich als Funktion der thermischen Zyklen deutliche Unterschiede in der Lötstellenfestigkeit
ergaben, außerdem wurde auch die Zuverlässigkeit des verwendeten Materials beeinflusst. Mit neuen Löttechniken wie SelectWave und MultiWave für bedrahtete Komponenten in Durchkontaktierungen ist es nötig, für die Qualität und Festigkeit der Lötstellen im Vergleich zu herkömmlichen Bleifrei-Wellenlötverfahren Referenzdaten zu gewinnen. Der Lötprozess beeinflusst entscheidend die Baugruppenqualität, charakterisiert durch Lotfluss in der Durchkontaktierung, Brückenbildung, ungelötete Stellen, Lotperlenbildung usw.

Enter product data

Process optimization: A case study for low defect
wave and selective soldering processes.

This research takes an in-depth look at the challenges encountered in developing a lead free wave soldering process based on the specific products as well as on specific materials.

Two major issues affecting the soldering process today are the conversion to lead-free soldering and miniaturization.

Quality of wave soldering depends on control of its many parameters.
A column written by Gerjan Diepstraten

By Ing. Gert Schouten, Senior Soldering Process Engineer, Vitronics Soltec

Introduction
Pad lifting and crack formation at the surface of solder fillets on plated through-hole solder joints was an issue in the days when boards were soldered at ‘Solder Cutting Solder’ lines, common in the 1980’s. The use of lead-free solder alloys today has brought about a recurrence of this crack formation, called fillet-tearing. There appears to be no cure this time; changing process parameters hardly provides any improvement

By Gerjan Diepstraten, Vitronics Soltec BV, The Netherlands

Abstract

European electronic manufacturers are currently testing and implementing lead-free solders in their production environments, in order to comply with a European Union directive that mandates the elimination of lead from electronics manufacturing in 2006.
For the majority of the assemblies the lead-free solder implementation will not have a big impact. It has been proven already that for a number of applications most of the work is required for changing the bill of materials and logistics, where for the process after redefining the most optimal settings, the soldering is done with equal or better quality results.

The implementation of a lead-free reflow process with alloys having higher melting points offers many challenges. One of the main issues is the optimization and repeatability of the reflow process within the specifications of the lead-free paste and components. The result is a narrow reflow soldering process window, which typically requires current reflow soldering equipment to decrease the conveyor speed in order to meet the materials specifications while still producing a reliable solder joint. This scenario has two consequences that compromise the manufacturer’s ability to produce an acceptable end product. The first and most obvious is that throughput is reduced. This compromise may be unacceptable but ironically, also necessary. The second compromise, one that depends on board complexity, component selection, and oven type is the exposure of materials to higher temperatures for longer times with minimal tolerance levels. Small deviations in the reflow process, while insignificant in SnPb processing, may lead to increased defect levels in lead-free processing.