Cleaning after repair.

Hi Randy,

No-clean flux needs to be activated in order to burn off the volatiles in the flux. This normally occurs partly during preheat and certainly during the reflow or soldering process. In most hand soldering applications, an operator applies liquid flux in excess onto the board. The soldering iron heats the area to be soldered, the volatiles are burned off where the iron�s tip contacts the flux. Problem is, in most cases, too much flux is applied, specifically to areas not in direct contact with the soldering iron. The flux is left unaltered on the board where it remains conductive and corrosive. This is why you have to clean the board.

Spot cleaning using a chemical saturated Q-tip or wipe is OK if the board is rinsed free of the cleaning chemical. The only think worse then flux left on a board is cleaning chemical left on a board. Most cleaning chemicals are high pH, very ionic, and in many cases, corrosive. Great care should be exercised to remove the cleaning chemical from the board. In addition, cleaning a board with a chemically saturated wipe or Q-tip normally results in the dilution of the flux, not the removal of flux.

Your options are:

1. Spot clean your board using a Q-tip or wipe then rinse the board thoroughly with DI water.

2. Clean the entire board in a cleaning system and remove all of the no-clean flux residue. Your boards will be cleaner and cleanliness related failures will be eliminated.

Mike www.aqueoustech.com konrad@aqueoustech.com

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>If the flux was not activated (ran in another area of the board), the flux should be removed from the board. Any Comments? A: We agree. In order for its �benigness� to take effect, NC flux is affected by: * Type of flux * Amount of flux * Proper activation.

> To accomplish this you should wash the entire board (which we have washers for) A: Makes sense.

>If the flux was restricted to the area of repair, the flux can be removed with a q-tip and alcohol or another spot cleaner. Any Comments? A: We disagree. Points of discussion are: * Flux goes a lot farther than the heat from the soldering iron reaches. That isopropanol carrier takes that flux places you would not believe. We don�t know how you plan to �restrict the repair flux to the area of repair�. * Spot cleaners do not clean the surface. They spread the residues over a broader area and, so, make them less visable.

> I am concerned that if the flux and Terpine is not wiped from the board the Terpine could leave a residue. If so, is this residue harmful to the board? A: Your intuition is correct. Terpine and the flux res probably should be removed from your board.

Terpenes are derived from citrus peels or pine bark, and are common ingredients in various household cleaners and deodorizers. They are effective in removing flux from printed circuit boards and other similar operations. Terpine is a commonly used saponifier used in semi-aqueous cleaning. For instance, the Bioac line from Petroferm contains terpenes. As mentioned by an earlier poster, saponifiers have a pH of ~11 when diluted.

Terpenes are generally recyclable, are biodegradable, and effluents may have fuel value. The disadvantages of using a terpine include a low flash point, high initial equipment costs, may require a modification to the wastewater discharge permit due to increased oxygen demand, and could cause adverse respiratory effects in sensitive individuals.

Semi-aqueous cleaners can be a mixture of water and hydrocarbons, which require both a rinsing and drying step in the cleaning process. Common semi-aqueous cleaners include terpenes and other hydrocarbons. Some closed-loop cleaning systems are available to lessen these negative effects.

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