The TR7007 Ultra-High-Speed 3D Solder Paste Inspection System

The TR7007 automated solder paste system from Test Research, Inc. is an inline measuring system designed to provide very fast 3-D measurements of solder paste deposited on the pads of the circuit board. This inline machine is typically positioned between the stencil printer and the pick and place machine. According to studies, half of all surface mount build defects are caused by poor solder paste control in the stencil printing operation. The TR7007 machine inspects all of the paste placed on the pads of a circuit board. Since stencil printing is the first step in the surface mount assembly process, it is the correct place for inspections that can prevent poor connections as a result of small solder joints, lack of solder, and other solder paste errors.

This report will discuss the TR7007 in four segments: the performance justification, the technical requirements to perform a solder paste measurement on all the pads of a circuit board, the key technical elements of the measurement system, and the typical error conditions can be which identified.

High speed production lines can produce large quantities of expensive circuit boards very quickly. When you consider the reliability issue of misaligned solder paste, incomplete coverage, and smears of paste on the pad, having the perfect volume of paste perfectly positioned on the pads is critical for smooth, flawless surface mount production of circuit boards. The accurate measurement of the x,y alignment and volume of the paste is critical. Considering the operation of a high speed line two shifts a day, any rework can halt an expensive assembly line.

The process challenge is to assure that the paste is perfectly placed on all the hundreds to thousands of pads on a circuit board without slowing down the production line. Also, the operator must be provided with statistical process data to indicate trends in the coverage. To measure every individual pad requires a technology that can measure placement, coverage, and area at a rate of up to 171 cm2/s with an accuracy of 14 µm.

There are two common techniques to generate a three dimensional image of the paste, using a laser and a camera. The TR7007 series uses an "on the fly" fringe pattern scanning mode to generate the 3-D image. The basic inspection uses a camera based system with two lights to eliminate shadows. Using a triangulation principle and four-step phase shifting technology, the system measures the height, volume, and thickness of the solder paste and checks for bridging.

Visual images of the solder paste on the pads are presented in two ways: a 3-D grey scale image and a two dimensional color image. A microscopic version of the 3-D picture is also available, which is especially valuable for smaller components. For times when a problem condition may not show clearly in 3-D grey scale, a 2-D color image can convey stencil printing information very clearly (Figure 5-1).

The most common types of errors are slumped printing, bridging, scavenged printing, and peaking. Poor coverage is also common when the apertures of the stencil start to clog-up with solder paste (Figure 5-2). Without a measurement system, the task to examine each individual pad manually would be impossible.

Wherever possible, the precision, measurement, and repeatability of a production line should be built into the equipment rather than relying on operator inspection. Solder paste measurement was the last inspection to be automated because of the difficulty of a 3-D paste measurement at the high speeds required. The TR7007 has satisfied the requirement for a high speed inspection system with the necessary speed and accuracy.

For more information or demonstrations of the TR7007 ultra-high-speed 3-D Solder Paste Inspection System and other EMPF capabilities, please contact Mike Prestoy at 610.362.1200, extension 241.