A Library Management Cautionary Tale


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The library management of footprints, land patterns, or cells—however you refer to them in your ecosystem—is one of the most critical items in the foundation of any PCB or CCA design. When I was asked to write an article on this topic, so many thoughts and experiences instantly flooded my mind. After 30+ years of designing PCBs throughout the industry, I have my share of experiences and stories about footprints.

One particular experience stands out—a project that I consulted on several years ago. My friend Vino asked if I could support a project that he was about to kick off. I said sure, as I had worked with him many times before. We discussed the initial PCB layout details, and we noted the extremely tight, aggressive schedule he was up against.

As we were planning our attack, the topic of library part creation came up, as usual. But this time, Vino wanted to farm out the library efforts to a third-party company that was unknown to me. I voiced my concerns about using this resource, and the importance of library parts being accurate and correct. Vino assured me that we’d be okay because this company came with high recommendations from a trusted source. I trust Vino, so a few meetings later, everything was put into motion.

The design at hand was a small, complex backplane card targeted for the end-product to go to a data center customer. The PCB measured 8” x 3.” It had 14 layers, 0.062” thick, with about 1,000 parts, and eight cluster modules containing 2 x 2.5 Gbps per link on each of these modules. This is a high-speed digital design, with around 40 Gbps data rates and very fast edge rates. It also featured two additional daughter cards, two network switches and a backplane controller BGA consisting of several hundred pins. The team worked like crazy and hit all the initial targeted phase gates within the project schedule. After lots of analyses done on the design, including a final DFM check, the design went out for fabrication as scheduled, with no apparent issues. Happy ending! Or was it?

About four weeks later, I was at the office when Vino called my cellphone. I answered, expecting to hear some early success of initial testing of the assembly. But I knew something was wrong from the tone of his voice. “Steph, I need your help!”

My heartbeat quickened. Vino proceeded to tell me that upon powering up the CCA, it got extremely hot within a few seconds, especially the backplane controller BGA. He had already powered up two of the five CCAs we had built, and each had this similar issue. We scrambled, discussing possible issues that caused the overheating.

To read this entire article, which appeared in the February 2021 issue of Design007 Magazine, click here.

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