Saving Water Plating PCBs

Article From: Products Finishing, , from Products Finishing

Posted on: 7/1/2000

A new manufacturing process at Allied Signal required clean-room technology and high-quality rinse water, increasing the rinse water flow rate. But, the company was able to reduce costs with the addition of a special treatment system...

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Flow Schematic

1. Flow Schematic for Rinse Water Treatment

The Allied Signal Substrate Technology and Interconnects Division of Honeywell Corp. was a conventional printed circuit board manufacturing facility. In 1997, it introduced a new product, flexible integrated circuits. These flexible integrated circuit boards are used in all types of consumer products, including cellular telephones and wireless hand-held and communication devices.

Although the new product would be similar to circuit boards, the manufacturing process would require clean-room environments with 100,000 and 1,000 ratings and high-purity rinse water of 10 to 12 mega ohms. Also, the rinse water flow would be much higher per rinse tank than previous levels. The requirement of high flow rates motivated the Process Engineering Department to recycle most of the water to reduce sewer connection charges and reduce waste treatment operating costs.

A new facility was built in Costa Mesa, CA for manufacturing the new product. Honeywell decided to invest in the new project because it was a new and growing market with high growth and earnings potential.

The Challenge

The composition of the waste streams was expected to be similar to any printed circuit board shop. The total flow rate was expected to be 125 gpm. This flow rate was a cause for concern for the company's engineers, since the regenerant concentrate from a conventional ion exchange recycling system would yield approximately 6,000- 9,000 gpd of waste.

"According to Vijay Desai, engineer at Honeywell, a large batch treatment system to treat the regenerant waste was unfeasible due to space constraints at the plant site. Moreover, any ion exchange system that created a large regenerant waste volume would not allow us to eliminate the sewer connection in the future."


TABLE I—PCB Water Treatment System Overview
Streams


Unit Operations
(125 gpm metal bearing)




Unit Operations



Recycle Metal Bearing

Regenerant

Footprint
Photoresist bearing (30 gpm)
Metal bearing (125 gpm)

Filtration
Oil and grease removal
Surfactant and light organic removal
Dissolved metal salt removal
Ultraviolet polish

pH adjust
Detackify
Filter press

>99%

Batch treated, discharged

48 × 25 ft inside the pit with same dimensions above. Above the pit includes feed tank, HCl and NaOH reuse tanks, two 2,000 gal batch tanks

 


In addition to treatment of the company's metal-bearing rinses, the company's engineers also wanted to treat the photoresist from the operations. Circuit board shops typically do not treat these streams, as they do not contain any toxic or regulated chemicals. Also, since these streams have high levels of organics, recycling them is not attempted. "Honeywell removes the photoresists using conventional chemical treatment and a decision is made based on a bench scale test as to whether or not a detackifier is used," noted Mr. Desai.

The first stage would be to treat the streams and discharge to sewer, once the treatment process was established, the treated streams would be combined with the other streams and recycled.

The streams were segregated as follows:

  • Developer stripper rinses to be treated for photoresist removal;
  • Tin-lead rinses to be pretreated for lead removal; and
  • All other rinses.

The Solution

The Hydromatix 786 System was selected based on the small volume of residual waste projected. For the 125 gpm flow rate and capacity, the system only generated 700-900 gpd of waste. This was 90% less than conventional technology. The system is designed to reuse rinse water from prior regenerations; minimizing generation of the regenerant waste. Therefore, a 1,500-gal batch treatment unit could be installed to handle this small volume as well as the periodic concentrated bath dumps. The system has been operating efficiently for more than a year.


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