SO14 package at 154C/W? Really?

If you ever do a garage sale and that FLIR camera is part of it let me know :-)

:-)

You will have to pry my thermal imager gun out of my 21.34 degree C dead hands.

John

I thought it was done, with X rays or something ?

It can be, and was more often when BGAs were new. There are also some optical things that can peek under the chips and let you see 4 or 5 balls deep, and also look for crud between the rows. We actually have one of those, and my production people sometimes use it, mostly to see that their temperature profiles look right, that the solder has flowed nicely. But once a process is up and boards are flowing down the line, individual board inspection isn't commonly done, by us or by our outside contractors. Like I said, we've scored 100% so far.

I think I could program a BGA to inspect its own solder joints, by measuring pin capacitance. Maybe I'll do that some day.

John

I'd suspect that board flex could be a killer in high-shock situations, or where a lot of force is applied by a heatsink clamp or some such. Gluing a fairly light pin-fin heat sink to the top of a bga FPGA doesn't seem very hazardous to me.

No problems so far.

John

I think that would work for signal pins on an FPGA, maybe even an ASIC if you had good JTAG.

I don't think it will work with power/ground pins. If, say, one of many power pins doesn't connect the chip will probably work fine in normal usage but might go flaky when adjacent pins are doing a lot of I/O.

Were those recent or back in the startup days?

I thought reliability was one of the reasons for shifting to BGAs. Consider the alternatives if you have a lot of pins.

Would you please ask your assembly people what they think about BGAs. I'd expect they work fine after they get the process debugged. There are a lot of them in use these days.

Yours are probably fine (and your customers seem to be technical folk who probably don't expect badly dinged hardware to still work). Some of our heatsinks weigh pounds apiece, and that 3000g test is no joke.

Cheers,

Phil Hobbs

We actually have a CT scanner for this up in Poughkeepsie. Takes a pretty long time when there are high atomic weight metals in the way, so iiuc it's used for sample testing and failure analysis--hopefully the failures happen during qualification and not in the field!

Cheers,

Phil Hobbs

Last case was in 2007.

I am self-employed and most of my clients farm out assembly.

Sometimes you've got no choice, like where there are 400+ contacts. But I try to stay away from such monster chips in my designs. I find that gull-wing contacts take flexing and G-force in the most graceful manner.

I don't know if you've worked in hi-rel design: System goes onto a launch pad, lifted x feet, dropped, crashes onto concret surface, lifted x feet again, and so on. Once in a while someone pours on another layer of concrete because the previous surface has hammered itself farther into the ground. After a while they protrude into the soil like stalactites.

What's your impression so far with respect to BGA versus PQFP and others?

Depends on the customers. Remember that ad picture in EE Design or something where a missile test went wrong, big fire ball, little arrow points to small black box up in the air, all dinged up? "This is one of our power supply modules and afterwards it still worked!"

I don't know--we basically don't use any packages with leads!

I can tell you that 32x148 pin surface mount connectors are hard to use.

Cheers,

Phil Hobbs

Not jtag. I was thinking of programming the fpga to put a weak pullup on all pins. Then pull a pin low and turn it loose and see how long it takes to go high. An unsoldered pin will have very little capacitance, so will go high pretty fast. Done right, this could catch all opens and shorts on all the i/o pins, without the need for jtag gadgets on the other ends.

Essentially none of the things we connect to fpga's have jtag of their own.

Maybe so.

John

I bought an anodizing kit from Caswell.. hopefully sometime in the next year I'll get around to trying it out.

Justifiable!

Cool. Best regards, Spehro Pefhany

Yeah, it used to be that "you can't base a company on a product", which meant that you had to have a grand scheme and a product line with critical mass to reach a market. Now, one person, with one good home-brew product, an assembly line in a garage or a big closet, and a decent web site, can get started and sell and grow. And a small company, using mostly free press releases and a keyword-loaded web site, can be as visible in some specialties as Tek or Agilent. The levelling power of the search engine is astounding.

John

What the heck do you use for a mating connector?

A male version surface-mounted on the backplane. ;) That's the standard backplane connector for the current P- and Z-series machines. Half of the pins are grounds, so for signals it's only 16x148. There's a _big_ preload put on it before reflow. (Yes, I realize that this is a ridiculous connector. That's one reason we're trying to move towards optical interconnection.)

It's been quite educational working in the packaging research area, even though I don't personally do any significant amount of electrical packaging work. You pick up stuff by osmosis and from people's talks.

Cheers,

Phil Hobbs

It sounds like the wrong place, in the system, to interconnect.

RL