Monday, August 29, 2016
VOLUME -24 NUMBER 7
Publication Date: 07/1/2009
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ARCHIVE >  July 2009 Issue >  Special Features: Assembly and Packaging > 

Using In-Line Cleaners for MIL PCBs
Six individual sets of tests.

Conventional in-line cleaning is giving way to specialized spray in-line cleaners for certain applications that have stringent environmental and MIL reliability requirements.

A typical example of this change has taken place at Astronautics Corporation, a manufacturer of military and commercial electronics in Milwaukee, Wisconsin. The company has been successfully using FAST® Technology based ATRON® AC 205 in a spray-in-air inline cleaner. To replace the existing inline cleaner, the company decided to evaluate the performance of Speedline Electrovert's AS 200 and the new AS100Ci inline cleaning equipment to enable it to select the right piece of equipment to meet its needs.

Astronautics Corporation also decided to test a competing cleaning agent from another supplier during this inline cleaner evaluation and wanted to finalize the decision on the equipment and the cleaning agent based on the test results.

Cleaning trials were conducted using both AS 200 and AS100Ci inline cleaners at Speedline Electrovert's facility in Camdenton, Missouri. For the cleaning trials, Astronautics decided to use standard double-sided test boards populated with 1825 and 1210 components. The test boards were soldered with AIM 291 RMA solder paste on upper side and Alpha 615 RMA flux on the bottom side.

Competing Chemistries
The wash temperature as well as the belt speed was pre-selected by Astronautics and the most appropriate cleaning solution concentration was suggested directly by Zestron and the competing chemistry supplier. Zestron decided to use ATRON AC 205 at 10 percent concentration while the competing product was used at 15 percent concentration.

The same process settings (concentration, wash temperature, exposure time and pressure settings) were used during the cleaning trials in both AS 200 and AS100Ci inline cleaners to provide an equal comparison.
Individual value plot responses for 4 test sequences.


Six individual sets of tests were performed for both cleaning agents in both inline cleaners. Multiple test boards were used during each set to check for the repeatability of the cleaning results. The boards were visually inspected to check for presence of flux residues on the board surface as well as underneath the components. All components were removed from the board surface. One set of boards was also subject to the ionic contamination test. The visual inspection was performed by two different technicians to average the subjective cleanliness assessment.

Trials with AS 200 with belt speeds low, medium, high: The first set of cleanliness inspections were done for 1210 chip capacitors in the AS200 equipment. As all tests were conducted at different belt speeds and two different orientations, six data points were collected for two different orientations. Differences between the two cleaning chemistries were only apparent at the lowest belt speed setting. The percent flux removed was found to be at 87 percent (SMT side up) and 32 percent (wave side up) versus 77 percent (SMT side up) and 30 percent (wave side up) respectively.

Maintaining an Advantage
For 1825 capacitors a similar result was found, although with slight modifications, overall cleanliness levels were higher. ATRON AC 205 at low belt speeds was able to remove 88 percent of flux residues for assemblies with the SMT facing upwards and 67 percent with the wave side up, whereas the competitive product achieved slightly lower levels of 74 percent flux removal with SMT up and 68 percent with wave side up. Increasing the belt speed to medium did not greatly reduce cleanliness with either chemistry. On average, the AC 205 maintained a slight advantage in visually-assessed cleanliness, although the differences between means were often well within the within-group sample variation.

Trials with AS 100Ci with conveyor belt speeds low, medium, high: Switching machines to the AS100CI, the results for both the 1210 and 1825 components were consistent with the AS200. The belt speeds for the AS100Ci were set to achieve the same process time in the wash section, so this result confirmed that the AS100Ci had equal spray effectiveness, given equal wash time (but slower belt speed).

When ANOVA was run on only the machine type, chemistry, and belt speed variables (and their interactions), neither the machine nor chemistry main effects nor their interaction achieved statistical significance.
Speedline/Electrovert AS100 cleaning system used in cleaning tests.


At 10 percent concentration, the overall test results showed equivalent to and slightly superior performance of ATRON AC 205 when compared to the performance of the competing cleaning agent tested at 15 percent concentration. This represented a 30 percent reduction in active concentration. For the most difficult cleaning challenge — the 1210 resistor, the AC 205 showed slightly better cleaning effectiveness at the lowest conveyor speed.

To compare the newly evaluated cleaning process with their current cleaning process, Astronautics Corporation decided to run one additional set of test boards and compare the ionic contamination values with AS 200 & AS100Ci process. For the customer the internal pass-fail limit was set to 14µg/sq.in. The ionic contamination results yielded lower values (less than 1µg/sq.in.) for both AS 200 and AS100Ci process compared to the current cleaning process. Based on the cleaning results and the overall performance, Astronautics Corporation decided to continue using ATRON AC 205 in its new inline cleaner. Zestron America provided onsite technical support during the cleaning trials at Speedline Electrovert and later at Astronautics.

Contact: Zestron America, 11285 Assett Loop, Manassas, VA 20109 888-999-9116 or 703-393-9880 E-mail: m.sachse@zestronusa.com Web:
http://www.zestronusa.com

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