Replacing a surface mount processor.

[Dave Plowman (News)]

I have a Megasquirt aftermarket car ECU with one of the injector circuits dead. Turns out to be the daughter board with the processor on it. Substituting the board sorts things, and probing with a scope shows no pulses on the board output for that channel, while the other is ok.

The board costs approx 120 quid in the UK

The processor itself is a surface mount 48 pin 0.5mm lead spacing chip in a 7x7mm package - which I can buy for 20 quid - so I'd like to have a go at replacing it.

I do have a hot air rework station - but have never attempted anything this complex.

Anyone give me chapter and verse on how to?

[Chris Bartram]

Not done it (yet), and I'm only doing a few simple components but I found this guide that looks OK:

[The Night Tripper]

Have a look at these (video) tutorials:

Essentials IMO (I use a fine soldering iron, not a hot air station) are:

- flux pen - loupe or magnifying lamp - tweezers - copper desoldering braid

Once you've got the knack surface mount soldering is not too dificult.

HTH Jon N

[Graham.]

+1 to that, I have seen 100 pin SMT chips replaced with conventional techniques. Specifically the infamous "Painter" chip that caused problems in so many Philips CRT TV sets.

[alan]

Ball grid component or leaded?

Search Youtube

Examples:

Don't forget that you are not trying to save the component you are removing so sometimes cutting the legs of some types of surface mount components does less damage when removing, although 7x7mm may come of quite easily.

A tin of flux or a flux pen will also help.

[John Walliker]

On Feb 9, 4:07 pm, "Dave Plowman (News)" w rote:

One useful trick is to cover all the nearby components with adhesive kapton tape so that they don't get blown away. Unfortunately a roll of kapton will cost nearly as much as the new chip, but it is really useful stuff. It is unaffected by soldering temperatures.

Something else which helps is to heat the board on a hotplate to a little below solder melting temperature so that you don't need to cook the chip so much in order to melt the solder.

Use plenty of flux both when desoldering and replacing.

John

[Lee]

This is a reasonable discussion of the "drag" technique:

Lee

[John Rumm]

There are some links to some good videos in:

For removing the old device, is often easier to run a sharp knife down each side of it a few times to sever its pins. That allows the bulk of the device to come off the board, and the pins can be flicked off with a hot iron after.

Failing that, hot air with the right nozzle, or one of the non eutectic alloy solder removal techniques like chipquick work well.

[robgraham]

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Useful thread - thanks guys. Some bookmarking for a later day when no doubt I might have to try this. Rob

[Peter Parry]

It's a bit like plastering. It takes 30 minutes to learn all about it and only another 20 years practice to get it right.

If you want some scrap surface mount PCB's to practice on I have plenty.

[Dave Liquorice]

+1 I surprised myself doing a 16 pin chip the other month. Had watched a few youtubes on the technique and it was surprisingly easy. Flux was non-acid plumbers flux, held chip in place with selotape, 15W non-temperature controlled iron and magnifying lamp.

[alan]

Is it blank processor with an external memory holding the code or is it something like a PIC (Peripheral Interface Controller) where the boiler manufacturer has embedded his own unique code in the integral non volatile memory? While the device may be available off-the-shelf the programmed device may not be.

[Andrew Gabriel]

I used to use a magnifying lamp, but found it easier to buy a £1 pair of reading glasses, 2 diopters more than you need for reading. Just been doing a load of surface mount capacitors...

[Dave Liquorice]

I'm -5 ish for distance already and am now having trouble with presbyopi a (age related long-sightedness). Without glasses I'm almost fixed focus,

maxium distance is about 8" minimum 6". Varifocals are wonderful. B-)

[Dave Plowman (News)]

Only seems to cover quite simple components like an op amp. The one I'm replacing has closer spaced pins and a lot more of them. ;-) It's a 7mm square chip with 12 legs on each side at 0.5mm spacing - a total of 48.

I've done some with more simple components. This is something else.

[Dave Plowman (News)]

What was the pin spacing? 1mm is ok with a soldering iron - but this is

0.5mm.

[Dave Plowman (News)]

That's given me some hope. ;-)

[Dave Plowman (News)]

It's a MC9S12C64CFAE. Megasquirt is open source and what descriptions I can find of the actual processor don't mention any unique embedded code. Uploading the various codes MS use is a user task.

[John Rumm]

I find the fine pitches are doable with drag soldering techniques...

Basically breaking many of the "normal" rules - so applying solder to the iron not the work, a big wide tip that is way too big to get close to a single pin, and loads of flux on the board first, then draw the iron along the row of pins hoping it all sorts itself out on the way!

[Paul D Smith]

I find the fine pitches are doable with drag soldering techniques...

Basically breaking many of the "normal" rules - so applying solder to the iron not the work, a big wide tip that is way too big to get close to a single pin, and loads of flux on the board first, then draw the iron along the row of pins hoping it all sorts itself out on the way!

+++++++++++++ There used to be some examples on the web of adding an extra 64MB memory chip to an Xbox v1 which used this technique. Could be useful as an example for you but I suspect the spacing might be more than 0.5mm.

Paul DS.

+++++++++++++ Windows Live Mail 2012 - No auto indent possible!