Reverse polarity, Scotty.

Remember: CE means "Can't Enforce."

The problem is with the production boards. To save agita, it would be nice to avoid a board spin unless there's something else wrong. It's quite a small-volume device (part of a much larger and more expensive system).

The Schottkys aren't for speed--they save me a volt of drop in the bridge rectifier. Otherwise, what with the 5% power supply tolerance and the droop due to charging up the capacitor, pull-in may be a bit marginal in corner cases.

I can make K1 a 9V relay, but those aren't as widely stocked as the 12V ones. I'll use BAV99RWs for now and switch back to BAT54Ses if we need a board spin anyway.

Thanks

Phil Hobbs

How about a stiffener for the other side of the board, with some stress members, e.g. like this:

Cheers

Phil Hobbs

I don't know the details of your circuit, but one option to consider is to design the board to be washed in 70 C water, solder using a water-based flux, and wash the completed boards off in a domestic dishwasher using AlcoJet detergent (or equivalent).

Joe Gwinn

Thanks. It's this ridiculous 50 gigohm front end (relevant portions posted upthread).

Cheers

Phil Hobbs

Can you put pads both top and bottom? Maybe only 10% compression on each side? (D@mn the expense and full steam ahead.)

George H.

I've never had any luck bending the leads on those little SMT packages- they tend to break right off. I'd stick it on upside down with blobs of solder re-inforced with little single strands from stranded wire, if necessary. Okay for up to a few dozen pieces, with some small loss in dignity, reliability etc.

Best regards, Spehro Pefhany

Excellent idea. I will forward it to their engineering team and, of course, give you full credit.

I was about to say, keep clear of water-soluble flux!

On a sunny day (Tue, 10 Sep 2013 09:39:45 -0400) it happened Spehro Pefhany wrote in :

Yes, and I actually unsoldered just such an 8 pin with bended up leads (connected to some SMDs) from a ground plane. Never expected it to come out with all pins still on it. but it did. µPB1505GR, 8 pin SOP, :256 prescaler.

No, there are all sorts of parts on the top, and the top cover of the box slides on/off horizontally.

The silly thing is that I proved to them that the d@mn thing is fine, thermally, as designed. Somebody put their finger on the FPGA, thought it felt hot, and things escalated.

I note, in passing, that most peoples' instincts about thermal things, suck.

That does nothing. The schematic already has the anode and cathode clearly marked. The real problem is that the pick-n-place machines can't read the schematics, only the footprint.

I've seen leads pulled off components but no failed solder joints. The gloom and doom from five years ago was that commie solder wouldn't make a year without tin whiskers. None so far.

They should be reading the CAD file. Older ones needed a XYRS file for that.

ote:

t thermal

rom a pcb,

wants

o chip and

h side? (D@mn the expense and full steam ahead.)

Oh my.. tell me about it! (no thermal instincts) I keep trying to 'wash my hands' of the current project. (I worry a bit that it'll get me fired.) At the heart is a LN2 cryostat. My boss thinks more mass is better, 'cause then the temperature will be stable... As it stands now the probe must hav e several pounds of copper. Byzantine layers are added to try and correct a 'flawed' design. I guesstimated a time constant of ~1000 seconds with 10

George H.

According to Hughes it even brought down one of their satellites:

That's precisely the problem. The CAD file assumed pin-1 was the cathode and pin-2 is the anode ("the standard says so") - the schematic symbol matches the vendor catalog => the component is backwards.

It was "fixed" by renaming the pins 'C' and 'A', everywhere. No confusion.

...and they know the lead wasn't pulled out, because?

Ouch. Air gap and long creepage paths.

I'd rinse the still-hot units fresh from the dishwasher in deionized water, then alcohol, and then dip in hot wax, to yield a hydrophobic conformal coating.

I assume that the PCB layout has guard rings et al.

I recall that the old Tek scopes were designed to allow them to be washed with hot water, to get all the dust and salt off the circuitry. The service manual gave the instructions. One did this once avery few years. Greatly reduced drift.

Joe Gwinn