Software plays role in solder-paste inspection

Many companies employ some kind of inspection to verify process steps within their surface-mount technology (SMT) lines. Because solder-paste volume is an important predictor of solder-joint quality and long-term reliability, performing solder-paste inspection (SPI) can help you reduce print-process solder-joint defects and, thus, save money by reducing the amount of scrap.

When evaluating which solder-paste inspection system best accommodates a particular manufacturing situation, be sure to consider the system's software. In particular, you should thoroughly investigate the CAD-conversion time and accuracy and the inspection-algorithm programming time.

CAD systems use a variety of commercial and proprietary formats, and this can complicate CAD conversions. The good news is that the CAD conversion steps needed for solder-paste inspection prove less daunting than those for post-reflow optical inspection or automated x-ray inspection, because the standard Gerber information used to cut the solder stencil is typically available and accurate. In the worst case, you can obtain the exact information from the stencil vendor to guarantee a match.

Fig. 1. Ensure proper pin designators and pin numbers for the inspection step.

Be sure to ask the vendor of the inspection system several questions about the CAD-conversion software:

• Does the software ensure proper pin numbering and give information down to the reference designator level?
• Is pattern teaching necessary?
• How fast is the translation process—what are the import and export speeds?
• Is the interface easy to understand?
• Do you have to learn a CAD package for each inspection system, or can you leverage your CAD-conversion package across your test portfolio?
• Is the software an added cost on top of the system cost?
• Do you have to purchase CAD for each item in your test and inspection portfolio (and associated training classes)?

Once the CAD information is converted, the engineer must program and fine tune the solder-paste inspection algorithm. Because of their high-volume production requirements, automotive-electronics manufacturers must minimize down-time for test and inspection-system programming. With today's systems, the entire process from CAD conversion through programming and fine tuning can take as little as 1 to 2 hrs.

Fig. 2. The Agilent software allows the programmer to set thresholds for each measurement of interest.

This example includes only a finite number of settings. The Agilent software also includes a drop-down menu (not shown) that allow users to dial into submenus of the same settings to make more specific changes. By allowing fine tuning, the globals and groupings do not trade-off program flexibility for programming speed.

Before settling on an inspection system, make sure you fully understand its programming features. Ask:

• How long does the average program take?
• How many algorithms need to be trained?
• How many settings need to be changed?
• Is the programming done by groups or does each pad require training?
• Can you set global parameters?
• How many menus must users learn to program the system?

The high throughput and unforgiving quality targets of automotive manufacturing represent considerable challenges. Using these lists of questions as a starting point when evaluating inspection systems will help you make the right decision for meeting those challenges.