* With the Holiday season fast approaching we will be staying close to home and planning our schedules for 2010.

* The Foresite offices will be closed November 26^th and 27^th for Thanksgiving. We will also close December 24^th and re-open January 4, 2010.

* The staff at Foresite wishes everyone a Happy Holiday Season!

Under-Cured Soldermask Porosity

In a recent client study, we observed that under-cured soldermask samples were absorbing extraction solution. Steam extractions, along with bag extractions, were performed using the C3 (Critical Cleanliness Control). At each localized extraction site, a visible color change occurred on the board surface, highlighting the potential problem. Figure 1 depicts the bare board prior to the C3 extraction. Figure 2 is the same location after the C3 extraction.

Three groups of bare boards were evaluated utilizing the C3 and ion chromatography (IC). The groups included: 1. bare boards from inventory, 2. no-clean fluxed and wave-soldered boards, and 3. bare boards exposed only to wave-solder with no flux. IC data on the bare boards showed high levels of sulfate and ammonia. The boards also had a visible color change at the extraction locations. The second group of boards (no-clean fluxed and wave-soldered) had high levels of chloride, sulfate, WOA (Weak Organic Acids), sodium and ammonia, and also exhibited the color change. The group of boards that were wave-soldered without flux had no visible color change and IC results were within Foresite recommended cleanliness limits.

Heat was applied for fifteen seconds, with a heat gun, to the boards with the color change. The additional heat appears to have improved the cure and minimized the mask porosity. After heat, ten lines were cut into the mask and they were re-tested with IC. Data indicated low levels of chloride, sulfate, WOA, sodium and ammonia. The mask color also returned to dark green.

Under-cured soldermask can be a problem if the water-soluble flux is not properly cleaned, allowing corrosive flux residues to become trapped in the mask. Once trapped, the residues are difficult to clean using deionized water or a batch cleaner. Initial indications are that the C3 is capable of detecting porous soldermask and identifying levels of ionic entrapment in the mask. Optimizing the soldermask cure is critical in reducing the mask porosity and ionic contamination.

Foresite is in the process of starting a user group for our customers with C3s. We have made attempts in the past to initiate some form of correspondence to answer your questions, provide helpful hints, or let you know of upcoming developments with the C3; now we hope to put a system in place that allows for better communication.

We are excited about new developments and changes forthcoming with the C3 and hope to keep you informed, as well as, solicit your input.

If you have a C3 or are interested in more information contact Eric Camden at ericc@residues.com.