Linear division in early 20th century

[Sub MandrelParticipant @submandrel]

Hi Andrew,

Tell me about it… my current project uses an accelerometer chip with 14 pads, all underneath it and it's about 4mm long. dwarfed by the Mega8 ina DIP next to it

Biggest chip I've done is 64-pin smt at 0.5mm spacing.

Neil

[Anonymous]

Hi Neil,

An accelerometer from Analog Devices? I used the ADXL321 a few years ago in a small unit designed to monitor vibration as a means of preventing 'Whitefinger'; nerve damage in the fingers caused by using vibrating machinery. It was a small ceramic package with all the pads underneath including one in the middle, a real PITA to solder by hand; sound familiar?

It seems to be an increasing trend to have a central pad underneath surface mount ICs. They're good from a mechanical point of view, and really help with thermal management and EMC on switchmode power supplies. But they're difficult to solder to by manual means. Unfortunately a lot of the pads now double as GND connections and must be connected.

Over the years I've developed my own techniques for soldering fine pitch SM ICs; what method do you use?

Regards,

Andrew

Edited By Andrew Johnston on 07/04/2012 12:11:08

[Ian PParticipant @ianp]

This thread seems to cover several enginnering disciplines unrelated to the original subject, so, on keeping with the trend, this post is as much On Topic as OT.

I was notified by email of Andrews last post. The emails usually contain the complete contents of the new posting, however the email this time included a sentence with a link to website. Interestingly this does not appear in the forum posting. Since Andrew edited the message after he posted it I presume he deleted it himself.

I suppose its something to bear in mind if one posts something and then later regrets it. Once it out there, its out there for ever!

Anyway, I use the 'flood and drag' technique when soldering something relevant.

Ian

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

A long time ago someone claimed in a magazine to have invented a solder equivalent glue . Never heard of it again but it does seem to me that a strong glue with good thermal and electrical conduction properties would be a useful thing to have .

Problem wih trying to devise one is that almost all common glues are poor conductors and so any practical mix would have to be heavily doped with conductive material which in turn would weaken the glue unacceptably .

A bit of lateral thinking needed .

If anyone out there fancies making a few billion pounds then see what you can come up with ..

[Ian PParticipant @ianp]

Posted by MICHAEL WILLIAMS on 07/04/2012 15:33:53:

A long time ago someone claimed in a magazine to have invented a solder equivalent glue . Never heard of it again but it does seem to me that a strong glue with good thermal and electrical conduction properties would be a useful thing to have .

Problem wih trying to devise one is that almost all common glues are poor conductors and so any practical mix would have to be heavily doped with conductive material which in turn would weaken the glue unacceptably .

A bit of lateral thinking needed .

If anyone out there fancies making a few billion pounds then see what you can come up with ..

'Lateral thinking', that must be what causes this 'Linear division in the early 20th Century' topic to only rarely be relevance to its title.

But keeping to the OT theme….. There is, (or was 12months ago) a 'glue' intended for use in the plumbing trade to join copper pipe and fittings instead of solder and heat.

I think it had a water like consistency and was sold in a tube ot bottle, it was claimed to be used with standard Yorkshire or endfeed fittings and be as secure as a soldered joint with both hot and cold potable water.

I have no idea of what chemistry or technology was involved or what its thermal conduction coefficent is. I wonder if it could be used to make a boiler for a steam model?

Getting back to one of the previous OT topics (semiconductors) there are electrically insulating materials for mounting power transistors etc on heatsinks that have significantly lower thermal resistance than the metal heatsinks!

Ian

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The idea was that such a glue could just be hand applied , screen or stamp printed onto pcb – contacts , grounding pads , heat sinks and fixings all in one go . Drop IC components into place and walk away – job done .

Very difficult to come up with a practical solution but certainly worth a lot to anyone that does .

[Sub MandrelParticipant @submandrel]

For the accelerometer I uses a cocktail stick to put tiny balls of solder paste on each pad, then dropped the part on with tweezers. Final stage was pop under the gril(!) until it setteld in place.

For ones with pins, such as SOICs, I tin the pads then go round with a very fin bit, gently pressing each leg down until the solder melts.

Unconventional, but they work.

Neil

[Anonymous]

Ian: Correct, I had second thoughts about the words and related link before posting and cut down the detail. After posting I had second, second thoughts and deleted the link. While details of the product are freely available on the manufacturers' website; it occurred to me late in the day that they may not be too happy about it being stated that it wasn't designed in their home country.

I've used two methods for hand soldering fine pitch leaded ICs. Fine pitch means 0.65mm and below; wider than that and it's easy to solder individual legs. In both cases I start by tacking the IC in place by soldering opposite corner legs. At this stage I don't worry about shorts between legs. I used to then flood the IC with a liquid flux. Then I'd get a big blob of solder over 3 or 4 legs. If you get the blob molten you can then pull it along the row of pins; each leg gets soldered and surface tension pulls the blob along without shorting adjacent pins. That's all very messy though. So I now just solder the whole row of pins, shorts and all, and then remove the excess solder with 'solder wick'. All the above applies to tin/lead solder, all bets are off with lead free solder.

Regards,

Andrew

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