Electronic Design

Bob's Mailbox

Hello Bob: I am looking for professional opinions/experiences regarding pc-board assembly using eyelets. I was told by Sam Reaves that you had written on the subject and could probably offer some good information. The problem that I am facing is that we are using eyelets on some pc boards in an effort to make the joints stronger. But I have seen some failures that are due to the eyelets. I need information to lead me to the correct decision and to use to convince others.

(Yeah, in my pretty good book on Troubleshooting Analog Stuff (p. 55), I said about 14 years ago that many people had given up on eyelets. They are unreliable when cycled over many cycles. Myself, I preferred to use double-plated-through holes, and I put wires through, and nobody ever argued with me that my solution was wrong, compared to eyelets. /rap)

I am of the opinion that the eyelets do not offer much insurance for a good solder joint, and in some instances they can and have become a liability. (You have shown that eyelets have lousy reliability. \\[That is a technical term.\\] It is not to put the onus on you to show that the eyelets are lousy. If the guys selling eyelets cannot show a mode of applying the eyelets to make them reliable, then throw them out in two minutes. /rap) What is your experience regarding eyelets and solder-joint quality? (I have had very little experience myself, but the guys who say they are bad have never been, to my experience, contradicted. The burden is on the peddlers, and I'd be surprised if they can beat it. /rap)

The application is an electronic lighting ballast. The pc board is single-sided, and the eyelets are used on the BJTs. I prefer plated-through holes, but because of cost they are not very practical. The eyelets were added to the BJTs because it was believed that they were one of the highest-stressed joints on the board, both electrically and mechanically in the manufacturing process. Because of the inconsistency I see with the eyelets, I think I may be better off with a regular nonplated-through-hole pc board. What is your thought on that?

  • Jason Cook

  • (via e-mail)

     

  • Pease: As you have a pc board where plated-through holes are not cost-effective, can you add wire stitches to connect through the board? Try some experiments. Add bigger foil lands for that transistor to bear the stresses and get the heat out. Your pc-board vendor must have some advice.

    Dear Bob: In your recent "Bob's Mailbox" (electronic design, Nov. 29, 2004, p. 20), you mention that the low-leakage diode trick with the 2N3904 (my favorite part) should leave the emitter unconnected. (The column I just wrote for the last issue uses 2N3904s, too \\[electronic design, Feb. 3, p. 18\\]! /rap) Why can't the base and emitter be connected together and still yield the low-leakage characteristic of the base-emitter junction?

     
  • Dave B.

  • (via e-mail)

     

  • Pease: It will do no good and no harm to connect the B to the E. But it is important not to connect the base to the collector. That makes an excellent diode, very fast (sub-nanosecond) with low leakage—but just for 3 or 4 V.

    Hi, Bob: Your column on "Merit Badge Stuff" (electronic design, Dec. 18, 2004, p. 20) inspired me to e-mail you. I earned the Electronics merit badge in the late 1970s. And the Computers merit badge, too. Funny that I ended up majoring in biochemistry for my first semester of college and then switched to EE. Been a professional EE for over 16 years now with only one month out of work last year.

    Now I think my nine-month-old son will grow up to be an EE, too. I just found out that he was born on Gustav Robert Kirchoff's birthday (March 24th)! Isn't this a great way to make a living? (Pointy-haired bosses notwithstanding.)

     

  • Jim Ford (via e-mail)

     

  • Pease: There are many ways to have a satisfying job in electronics! Even if you were—or weren't—born on Kirchoff's birthday. Best regards, and best wishes to your son.

    Comments invited! [email protected] —or:
    Mail Stop D2597A, National Semiconductor
    P.O. Box 58090, Santa Clara, CA 95052-8090

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