In a recent Design007 Survey, we asked the following question: Q. What is the most important feedback that you receive after your board is manufactured? Here are just a few of the answers, edited slightly for clarity:

• Scott McCurdy, Freedom CAD: We run all of our designs through Valor NPI, so we don’t have many problems get back to us. But more feedback from our customers would be helpful. We always like to hear when a customer is happy and the board worked the first time.
• Dwain Strang, ZIN Technologies: What came up at first article checkout? How did everything go together? Was testing OK, and did it pass?
• Alex Forbes, Rakon: That it works! Feedback from the manufacturer and the assembler.

One of the most interesting findings in IPC-2152 was that internal traces are cooler than external ones for the same size and current. Independent experimentation was not done on internal traces in earlier charts. Internal traces were merely assumed to be hotter than external traces, and the external trace data was derated by 50% by that assumption. Traces are heated by Joule, or I2R, heating. They are cooled by a combination of conduction through the dielectric, convection through the air, and radiation. It had previously been assumed that convection conducted heat away from the traces and cooled the traces more efficiently than conduction through the dielectric. Hence, the assumption that internal traces were hotter than their external trace counterparts.