Flux residue on connector pins

Chen,

It is always best to place one�s effort on determining the cause and content of the residue rather than trying to work around it.

The first thing you must determine is the nature of the residue. Is it flux? In many instances, the residue is not flux. There are many things it may be besides flux (metal salts, minerals, chemical residue, etc).

If it is flux, and the flux is soluble in water (OA), then why is it still on the connector? Questions to consider:

1. Did the wash system deliver heated water to all surface areas of the connector?

Suggestion: Check to see if shadowing is occurring. Re-arrange parts in your cleaner to ensure adequate spray coverage and maximum impingement.

Suggestion: If it seems that water is not penetrating tight spaces, consider the use of a chemical additive to reduce the surface tension (if your cleaning system permits).

Are you using DI water? If not, you should be. Use of tap water may result in residue.

2. Was the flux �burned on�?

Suggestion: Check your oven / wave / hand soldering profile. A frequent cause of flux or other residue is a very hot profile. In any soldering process, metal salts are formed during the reflow process as the flux reacts with the oxides on the board�s surface. These metal salts are normally encapsulated into the flux and are easily removed during the cleaning process. When a reflow profile is too hot however, higher temperatures increase oxidation and thus metal salts. Higher temperatures also reduce the flux�s ability to encapsulate the metal salts allowing them instead to adhere to the board�s surface creating a white residue and additional cleaning challenges.

Many forms of residue, once on the board, are very difficult to remove. In many cases, only mechanical action or re-reflow will remove the residue.

I hope this helps. Mike Konrad Aqueous Technologies (909) 944-7771 konrad@aqueoustech.com

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Hi Chen,

Based on your posted message, the following ideas are for your consideration:

"brown residue" The water soluble solder paste you are using could be a water soluble rosin solder paste formulation. Perhaps the solder paste may not be properly prepared or formulated, creating an inability to clean with water. If your process previously worked and then didn't, this could be a result of a variation in the batch of solder paste you are currently using. If this is the case, you should consider cleaning these boards with an aqueous mixture.

"on connector" If the residue is solely around the connector and clean everywhere else, examine the connector closely. Do you receive it clean, free of residues? As Mike says, is your cleaning equipment able to deliver good mechanical energy to the connector? Is there rework involved?

"wash again useless" Time and temperature are variables in your cleaning process to consider extending and raising. Also, consider draining and refilling your wash reservoir.

Best Regards,

Shean Dalton Austin American Technology www.aat-corp.com (512) 335-6400 sdalton@aat-corp.com

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