Tag Archives: IPC

Farewell, Dr. Jennings

Posted on by

Charles Jennings isn’t a household name – even to electronics engineers – but most every person who designs or builds circuit boards for a living owes a small debt of gratitude to him.

For it was Jennings, a Sandia National Labs chemist, who in the early 1970s conducted the research that led to the current carrying capacity charts that have been a staple of electronics design ever since.

As I wrote on the TechNet ListServ more than a dozen years ago:

Jennings’ report describes a series of tests to establish electrical properties. The results includes voltage holdoff, current carrying capacity and insulation resistance for two-sided bare, coated, and encapsulated boards.

Average breakdown voltage (V) followed the relationship

V = 3.1 S(superscript)0.51,

where separation (S) ranged from 0.25 to 1.5 mm.

(This is for bare boards at ambient conditions.)

Current carrying capacity of conductors was evaluated by temperature rise between conductors generated with step increases in current. Variations in temperature rise between conductors with the same nominal or design width were correlated with meaured

differences in conductor cross-sectional areas. Resistances calculated from conductor lengths and cross sectional areas were within 10 percent of the measured values.

The boards tested were fabricated using a panel plate and solder dip or plate and liquid level process. A few measurements were made on boards fabricated using a pattern plating process with thin clad laminate.

Testing was “frequently” extended until functional failure to obtain a better understanding of the failure mode.

IPC published the Jennings’ paper, “Electrical Properties of Printed Wiring Boards,” as IPC-TP-117 in September 1976.

The results of the study indicated that conductor spacing recommendations in MIL-STD-275 were very conservative and could be reduced. Yet the mil spec’s commercial equivalent, IPC-D-275 (known famously as Table 3-4), and later IPC-2211, all pulled from the original work.

Since then, several companies, including AMP, Hughes and Lockheed-Martin, tried to duplicate the measurements. Generally speaking, they discovered certain holes in the findings.

On several occasions, I have talked with Mike Jouppi, the heady and creative Colorado engineer who has been wrestling with Table 3-4 for a decade. It looks like Mike has won. This week, IPC published IPC-2152, which finally replaces IPC-2221’s conductor sizing charts. Now, almost 40 years later, it is only a matter of time until Dr. Jennings’ landmark work will finally be laid to rest. But let’s not let the inevitable progress of technology to sand over a truly remarkable history of utility, one from which we have all benefitted.

P.S. IPC has sold tens of thousands of copies of IPC-D-275 and its successors, all based on Dr. Jennings’ famous study. Yet Jennings never made it into the IPC Hall of Fame. Go figure.

Hunting Witches

Posted on by

In Europe, the fight against TBBPA continues, but at least this time IPC is on the right side of an environmental witch hunt.

The trade group yesterday issued perhaps its strongest statement yet on the matter, encouraging its members in Germany and Sweden to lobby their respective environmental agencies and government officials to keep Tetrabromobisphenol(a) legal.

In doing so, IPC broke with its recent history of abdicating difficult policy decisions. Faced with a proposed EU ban on lead and other primary elements, IPC took the position that it was a fait accompli, and chose not to rally its members to fight the proposed ban (now known as the RoHS Directive).

What’s interesting here is the similarities in the defense IPC is putting up. Then, IPC acknowledged the anti-lead crowd was using faulty science and that lead in electronics posed no risk to human health or the environment. Yesterday’s announcement, IPC wrote: “TBBPA is a popular flame retardant used in more than 80 percent of the world’s printed circuit boards (PCBs). A comprehensive EU Risk Assessment found TBBPA not harmful to the environment or to human health.”

It’s unclear to me why IPC decided to flip-flop on this one. But I’m glad it did.

What a Waste

Posted on by

All sorts of nonsense is erupting in our industry’s corner of the environmental arena this past week. Let’s go to the tape:

  • On May 14, Rep. Michael Burgess (R-TX) introduced a bill that essentially codifies the EU RoHS Directive for the US as well. The bill proposes to prohibit the manufacture after July 1, 2010 of “electroindustry products” that contain lead, mercury, cadmium, hexavalent chromium, PBBs, and PBDEs above the maximum concentration levels specified in the European Union’s RoHS Directive.
  • Today, the Electronics TakeBack Coalition issued a statement opposing a toxic e-waste bill scheduled to be introduced in the House later this week. The bill, sponsored by Rep. Gene Green (D-TX) (how’s that for irony?), Rep. Mary Bono-Mack (R-CA) and Rep. Mike Thompson (D-CA), permits e-waste exports under a loophole under which any type of entity can export toxic e-waste to developing nations for reuse and refurbishment, the Coalition asserts.

    “By passing a law that only appears to restrict exports to developing countries without actually doing so, the bill would undermine those recycling companies which are in fact managing their e-waste responsibly, and providing jobs here at home. This bill fails in serious and even critical ways.”

  • And in between, IPC issued a press release boasting how 22 of its 2700-odd members managed to trek to Washington in support of a permanent R&D tax credit, something that just about every technology company operating in the US already supports anyway — and many of which are priming the lobbying pump to ensure it goes through.

    So in summary, we have a Republican from Texas trying to overlay (absurd) European laws onto US manufacturers, an industry environmental advocacy group trying to shoot down new proposed environmental regs, and the major US PCB trade association completely in the dark about all of it.

    Not too good.

    • Apex or Bust!

    Posted on by

    Tuesday marks the opening of Apex, the largest electronics assembly trade show in North America. With it, the industry suppliers hope buyers will turn out in force for the Las Vegas event. The early returns don’t look promising, with suggestions that preregistration attendance numbers are down some 15% or more from last year, coupled with travel bans by several major OEMs. Here’s hoping this week marks not another nail in the coffin but the beginning of the turnaround.

    Tonight, CIRCUITS ASSEMBLY will announce winners of its NPI and Service Excellence Awards. Check back for frequent updates.

    A bit of early gossip: IPC will induct Dan Feinberg to its Hall of Fame on Tuesday. Years ago, Feinberg was president of the dry film and soldermask division of Morton (now owned by Rohm & Haas) and was a major driver behind the IPC Printed Circuits Expo trade show.