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62 SMT007 MAGAZINE I NOVEMBER 2020 of an NCMS program with Scandia National Laboratory, founders Tim Estes and Ron Rhodes licensed the testing machine from Scandia and started CAT in 1994. The test equipment and test methodology are patented under U.S. Pat- ent No. 5,659,483. Because of the length of availability, its thoroughness, and the wealth of publications, the CAT coupons are the most used and benchmarked. Six coupons, all 25.4 mm by 25.4 mm (1.0" x 1.0"), make up the primary sensors for CAT (Figure 3): 1. Conductor (spacing) 2. Via formation (nets daisy chain) 3. Registration (I/L and O/L) 4. New registration (I/L and O/L) 5. Solder mask registration 6. Impedance The value of a parametric system like CAT is its ability to capture the true capability of a process, procedure, machine, or materials. There are numerous features on each coupon such that they can be tailored to capture cur- rent capability. Complex as these are, they can- not be inspected or sorted, so they truly rep- resent what is going on. For novice users, the temptation is to inspect them to get per- fect samples. This usually proves to be a futile activity, as some features are beyond the cur- rent capability by design. These coupons are all customizable by CAT: conductor spacing (1–20 mils), via diameter, via land, daisy-chain sequence, number of layers, registration sensitivity and layers, via structure (through, blind, buried, skip vias, stacked, sequentially laminated, etc.), imped- ance type (single-ended, differential, edge-cou- pled, broadside, coplanar, etc.), overall thick- ness, placement, and panel size. Some coupons were designed to be removed and put in small testers. The ones shown have been redesigned, and you can see the new ones under test pat- terns at cat-test.info. The primary equipment is shown in Figure 3g. This was designed by Scandia and con- sisted of an alignment system, fixtures, and a bed-of-nails connected to a sensitive AC- chopped, four-wire Kelvin resistance measure- ment system (Figure 3j) feeding a PC. In 1999, a portable system was also designed so that readings could be made in production using an Agilent 34401A voltmeter shown in Figure 3 (h and i). The portable system has additional coupons from 0.33"x 3.0" to 0.5" x 2.0" to facilitate placing on production panels, as well as software, to automatically calculate responses. To improve the impedance mea- surements, the Polar RITS-510 robotic probe and measuring unit were added in 2003. The Hong Kong Productivity Council erected a sec- ond testing facility using this equipment in Hong Kong in 2004 [1] . Printed Circuit Process Capability, Quality, and Relative Reliability The popularity of the CAT panels eventually led to its standardization in 2000 by IPC. The D-36 Subcommittee created standard para- metric panels and a test standard that became known as IPC-9151 PCQR 2 . The data from these benchmarking panels is kept in a database available by subscription from IPC. Over 89 PCB fabricators worldwide have built PCQR 2 panels for testing. Artwork and specifications for these benchmarking panels are available to the industry for free at pcbquality.com. Fig- ure 4 shows a typical PCQR 2 panel, which is a 14-layer (IPC-14VB-D) via rigid board design (18" x 24") utilizing through, blind, buried, and sub-composite vias with two laminations. Figure 4 shows the complete list of available PCQR 2 panels. Highly Accelerated Thermal Shock One of the results of the D-36 Subcommittee's work on relative reliability was the creation of a highly accelerated thermal shock procedure. Developed by CAT and Microtek Labs, HATS TM runs the PCQR 2 coupons through an air-to-air thermal cycle from -45°C to 145°C (-60°C to 160°C available) in a 30-second cycle (Figure 5a). The coupons are continuously monitored by a four-wire data acquisition system con- nected to the test fixture (Figure 5b) to detect a 10% change in the resistance of the via daisy chains, or 500 cycles. The coupons can be various sizes from 0.5"x 1.0" to 1.0" x 2.0"