ELECTRONIC ASSEMBLY AND WAVE SOLDERING OPERATIONS

Last adopted: May 15, 1998

Electronic Assembly/Soldering is where electronic components are assembled and soldered onto printed circuit boards. The process steps include flux application, hand soldering, wave soldering, solder paste application with reflow oven, and solvent cleaning. The potential of pollutants into the atmosphere are Precursor Organic Compounds (POC). The Bay Area Air Quality Management District regulates these air pollution sources by imposing emission standards or organic content limits and by requiring Permits to Operate for selected electronic assembly/soldering processes.

This permit handbook chapter describes the permitting procedures for flux application and solder application. Permitting of solvent cleaning are covered by other Permit Handbook Chapters such as Wipe Cleaning and Vapor Solvent Cleaning. The first two sections of this chapter describe the types of processes that may be encountered at a electronic assembly/ soldering facility and the air emissions associated with these processes. The next two sections discuss Bay Area Air Quality Management District permit requirements for this industry and items necessary for a permit application. The fifth section is an engineering evaluation template and includes typical equipment descriptions, sample emission calculations, applicable regulatory requirements, and sample permit conditions.

I. PROCESS DESCRIPTION

The electronic assembly process involves the assembly of electronic components onto printed circuit boards. The following sections will discuss various methods that can be used.

A. Hand Assembly

This is where components are manually assembled and soldered onto printed circuit boards. The process steps include flux application and hand soldering.

B. Solder Paste Application/Surface Mount/Reflow Oven

This method involves the application of solder paste to pad locations on the printed circuit board through a stencil. Components are then surface mounted onto the printed circuit board with a pick and place machine. After inspection, the surface mounted components are joined to the printed circuit board inside the reflow oven.

C. Wave Solder

This method is where components are soldered onto the printed circuit board by a wave soldering machine.

II. AIR EMISSIONS

In the electronic assembly/soldering operations, POC emissions occur during the flux and soldering application because the flux and solder paste used contains organic compounds. Since many of the Bay Area Air Quality Management District’s permit requirements for this industry are based on the emission rates of precursor organic compounds or toxic compounds, these emission rates must be determined before the permit requirements can be assessed. Section A gives an example of an uncontrolled emission calculation and examples of controlled emission calculations with air pollution abatement equipment.

A. Sample Emission Calculations

Emission calculations are based on the maximum annual net usage rates of flux and thinner applicators. Assume all VOC contained in the flux and solder will be emitted to the atmosphere.

1. Uncontrolled Emissions:

Flux Usage 200 gal/yr

Density 6.6 lb/gal

Organic Solvent Content 85%, by weight

Organic Components 100% Isopropyl Alcohol

Thinner Usage 300 gal/yr

Density 6.5 lb/gal

Organic Solvent Content 100%, by weight

Organic Components 100% Isopropyl Alcohol

(200 gal/yr)(6.6 lb/gal)(0.85 lb/lb) = 1122 lb/yr

(300 gal/yr)(6.5 lb/gal)(1.00 lb/lb) = 1950 lb/yr

Total Yearly Emissions = 3072 lb/yr

Annual Average Emissions = (3072/365 day/yr) = 8.42 lb/day POC

2. Controlled Emissions, Carbon Adsorber:

Assumed Capture Efficiency = 90%, by weight

Fugitive Emissions = (8.42 lb/day)(1.0-0.9) = 0.84 lb/day

Exhaust Flow Rate = 500 scfm

Outlet Concentration = 10 ppmv max.

(10 ft3/106 ft3)(500 ft3/min)(1440 min/day)/(386.7 ft3/lbmol) =

0.01862 lbmol/day

Emissions are 100% Isopropyl Alcohol with MW = 36.07 lb/lbmol

(0.01862 lbmol/day)(36.07 lb/lbmol) = 0.67 lb/day

Total Emissions = (0.84 + 0.67) = 1.51 lb/day POC

Overall Control Efficiency 100 - (1.51 lb/day)/(8.42 lb/day)*100 = 82%, by weight

3. Controlled Emissions, Thermal Oxidizer:

Assumed Capture Efficiency = 90%, by weight

VOC Destruction Achieved = 99%, by weight

Fugitive Emissions (8.42 lb/day)(1-.9) = 0.84 lb/day

Oxidizer Emissions (8.42 lb/day)(0.90)(1-.99) = 0.08 lb/day

Total Emissions = (0.84 + 0.08) = 0.92 lb/day POC

Overall Control Efficiency 100 - (0.92 lb/day)/(8.42 lb/day)*100 = 89%, by weight