SO14 package at 154C/W? Really?

No, but I have seen too many BGA failures. Not in my designs because (with one exception) I never used BGA.

We just use regular epoxy, gently squished down.

Opposite experience. We've used hundreds of BGAs, mostly FG456's, nearly all placed and soldered in-house, with exactly 100% success.

The only one we've ever removed and replaced was a couple of weeks ago, and that was a mistake. There was a power plane short, nobody could find it, so somebody decided to remove the BGA. NEEP! That wasn't it. I dumped a 6-amp power supply into the plane and hit it with the Flir imager... sure enough, a ceramic cap glowed in the thermal IR... a simple solder bridge that nobody spotted.

We have a lot more trouble with TSSOPs and other fine-pitch leaded parts. US8's are the pits. One nice thing about BGA solder joints is that you can't inspect them, which saves a lot of production time.

It's liberating to have 200,000 gates and 300 i/o pins, in about a square inch, at your disposal.

John

It didn't know it was one of those. I'll say however than the max figure seems insane. Probably a left-over from an early data sheet revision.

Can you not use DIP or even SIL ? 5532's are available in SIL with a significant board area decrease. I'm actually looking for some at the moment since they're not widely known about.

Graham

:-)

Same here, MLFs and QFNs are just as difficult to deal with in production lines. We are skipping packagings all together. Chip On Board (COG) die bonding is just as easily to order as anything else, but usually 1K minimum.

It's even better to be able to define your own footprints. We are using a 68 pads die with 32 pins in one project and 44 pins in another. They are just die bonded differently.

Don't you mix up hazard analysis with worst case analysis here? If the data sheet says 16 mA and a part consumes only 8 mA over its operating temperature range, it will not suddenly start consuming 16 mA just because the data sheet says so. Depending on how many units you are going to manufacture you can always buy a lot of parts and screen out the ones exceeding your requirements, let's say 10 mA. Now use the measured values and add some margin due to ageing effects in your WCA.

If you are doing an FMEA and are afraid of the part becoming to hot and possibly causing a hazardous situation you anyway can't rely on the data sheet since during a failure the part can consume much more than listed in the data sheet. Thus you have to look at the current limit of your power supply and the thermal properties of all parts connected to that power supply that can generate hot spots in case of failure.

Dropping the board just once is often enough--the acceleration during impact is

a = g*(height of fall)/(crumple distance)

which can easily be thousands of times g, especially on hard floors.

Our server blades have to pass a 3000g shock test, which is really tough if there's no compliant layer (such as paste or liquid metal) between the HS and the processor. C4 balls are under a lot of static stress to begin with (although little ones with under 500 connections are easier than large ones).

Cheers,

Phil Hobbs

significant

not

No, only SMT. But why should I? The old Motorola amp works, uses a lot less power and ONSemi keeps making tons of them. Plus has ST as a 2nd source.

No cherry picking in this business.

I know, that's all in the hazard analysis. What I meant is that if you design in parts assuming "typical datasheet values" it's only a matter of time until the FDA has you over the barrel.

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

PSU

seems

significant

they're not

But I thought your initial question was whether the MOT part was suitable ? Yet the supply current is in the 100s of uA !

Where did you you get you 400 odd mW from ?

Graham

PSU

seems

significant

they're not

Yet the

But not 1000s of uA line the 5532.

I need another 2mA per output from each amp at almost 40V supply. Might be able to squeeze it down to 1mA or less.

It is not cherry picking if you write a proper specification with your specific values and buy the parts via an independent test house. They typically charge you a few dollars per device in test costs plus a fixed sum for the test setup. Could be worth looking into that alternative depending on your volumes.

This is the same procedure as the microprocessor manufacturers use, except that they do the screening in-house. There is no physical difference between a 2 GHz and a 2.4 GHz processor, it just happens that some wafer lots end up faster than others during manufacturing.

"a few Dollars per device" would be the killer here. Medical might be a lucrative market but not that lucrative ;-)

But then they are shipped with different part numbers. In medical you'd have to also laser-mark the devices. Anyhow, I really never do that but always look for a solution that works with off-the-shelf part. A solution which I now have, by using MC33171 amps. Same as the MC33174 but singles instead of quads. Cheap, works.

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.