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Not just for cosmetic reasons

Case study on service life of cleaning baths formulations for solder frames
Not just for cosmetic reasons

Wave soldering requires the board assemblies to be mounted onsolder frames to guide them through the furnace. As a result, the frames become contaminated with flux residues, PCB degassing products and solder mask material. Severe contamination causes negative impact on process reliability and assembly quality. Consequently, it is very important that these residues are regularly removed – not just for cosmetic reasons.

A cleaning process for solder frames at a Siemens facility in Munich/Germany involves immersion with an aqueous-alkaline medium in a Kolb cleaning machine. The cleaning agent used from beginning was found to no longer fulfill the increasing cleaning demands, and hence in a research action other cleaning agents were investigated. The performance of the liquid was verified according to the following experience:

• A bath life of only three to four weeks with the previous cleaning agent was unsatisfactory, since frequent bath changes gave rise to considerable expenses of work and costs. Moreover, the volume of cleaning agent that had to be disposed of throughout the year was remarkable high, thus incurring elevated additional waste disposal costs
• The other cleaning agent must have a significantly longer service life
Although the previous process removed the contaminants from the solder frames, they were recontaminated during the rinse in spite of frequently changing the rinsing water. The cleaning result was therefore not satisfactory, and the problem had to be overcome with a new cleaning medium. Also, the introduction of contaminants in the cleaning bath had resulted in an unpleasant smell that was no longer acceptable on the shop floor. Even with intense contamination, the new cleaner should not emit any smell or at least a more acceptable scent than the other one. The cleaning machine used was not in question. The change to another cleaning agent would for that reason require using the same machine. Furthermore, the new medium had to be well compatible with the solder frame materials.
Intensified by air
Zestron, a division of Dr. O.K. Wack Chemie, supplied the Atron SP 200 cleaning agent, an aqueous-alkaline medium specifically developed for the removal of encrusted flux residues from solder frames and condensate traps. This cleaning agent was used in a 15% concentration. During the first process stage, the solder frames were cleaned by immersing them in the medium for approximately 12 minutes. The cleaning action was intensified by blowing air into the bath (agitation). The frames were then manually transferred to the rinsing stage and watered for approximately5 minutes with tap water agitated by blown-in air. The final step was then to dry the solder frames with circulating air for about 13 minutes.
Selection criteria for the cleaning agent
• Significantly lengthened service life of the cleaning bath
• Good cleaning results
• No recontamination of the rinsing bath
• No smell
• Well tolerated by the solder frame material
• Suitable for use in existing cleaning machine
The cleaning results achieved with the improved process fulfilled all expected demands. All residues were reliably removed while material compatibility was found to be good. The high rate of dirt introduction from approximately 300 solder frames did give rise to bath foaming during the test. The addition of a small amount of defoamer solved this problem.
After the cleaning bath was filled for the first time, some 500 solder frames were cleaned during a period of eleven months without having to replenish the cleaning agent or change the bath. This means that the service life of the new cleaning agent was approximately 10 times longer than that of the media used previously, thereby significantly exceeding demands.
Reduced disposal costs
The number of batch changes required in the past has been drastically reduced due to the long service life of the new cleaner. The total volume of contaminated cleaning fluid has consequently been significantly reduced. Disposal costs of a contaminated cleaner are very expensive because of it being classified as a waste that has to be monitored. Cost reductions using a longer life cleaner are hence achieved from a savings on disposal as well as providing for a better environment.
The cost per cleaned solder frame was reduced to a fraction of the previous costs by reducing the cleaning agent consumption as well as less maintenance for the bath and reduced quantities of waste for controlled disposal. The user also confirmed that the smell of the new cleaning agent was far more pleasant, thus representing a significant improvement over the past product. The product is also classified as environmentally friendly and non-hazardous.
As a result of these positive marks, the company now uses the Atron SP 200 in its cleaning process. In addition to the solder frames, also the condensate traps from reflow ovens are now being cleaned in the same process.
ZUSAMMENFASSUNG
Den Wellenlötofen durchlaufen Baugruppen eingespannt in einem Lötrahmen. Doch auf diesem sammeln sich festgebackene Rückstände aller Art, beispielsweise Fluxer, Zinnreste, Ausgassungs-Produkte der Leiterplatte und Lötstoppmasken-Material. Selbstredend ist dies weder der Qualität von Prozess noch Produkt zuträglich. Nach Problemen mit einem Reiniger hat man sich nach einer längeren Testphase in einer Siemens-Fertigung für Atron SP 200 von Dr. Wack Chemie entschieden.
RÉSUMÉ
Les sous-groupes traversent les fours à braser à la vague fixés dans un cadre de brasage. Mais sur celui-ci s’accumulent des résidus brûlés de tout type comme du flux, des restes d’étain, des produits de séparation de la carte imprimée et des résidus du masque. Ceci n’est bien sûr dû ni à la qualité du processus, ni à celle du produit. Après des problèmes rencontrés avec un nettoyant, le produit retenu suite à une phase prolongée de tests fut Atron SP 200 de Dr. Wack Chemie.
SOMMARIO
I gruppi costruttivi attraversano il forno di saldatura ad onde in stato serrato all’interno di un telaio di saldatura. Ma in quest’ultimo si depositano residui attaccati di qualsiasi genere, quali ad esempio fluxer, residui di stagno, prodotti di degassamento del circuito stampato e materiali da maschere di stop saldatura. Ovviamente ciò non è proficuo né per la qualità del processo e né per il prodotto stesso. Dopo alcuni problemi con un detergente ci si è decisi dopo una fase di test prolungata in una linea di produzione Siemens per Atron SP 200 della Dr. Wack Chemie .
Current Issue
Titelbild EPP EUROPE Electronics Production and Test 11
Issue
11.2023
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