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[Martin_1962]

Small PCB like two layers stuck together with small joiners through it.

Doesn't work unless I squeeze the main chip at one end, can't see a bad connection - any ideas?

[TheBoy]

Inspect ssoldering with a decent magnifying glass.

[Marks DTM Calib]

Pics!  

[Martin_1962]

Will have to look for something digital with macro - but it is a keyfob

[Taxi_Driver]

Sounds like the layers are coming apart.......as its small....any chance of super glueing the end the pcb....whilst pressing on it until glue dries  :-/ :-/ If you can see if you can get the glue inbetween the layer before pressing on it.

[Martin_1962]

Can't see a gap but I need to solder a small wire from the main chip throught to the other side of the PCB

Not at all easy and all for £9 + postage

[TheBoy]

Can't see a gap but I need to solder a small wire from the main chip throught to the other side of the PCB

Not at all easy and all for £9 + postage

Have to sometimes take the rough with the smooth...

[Marks DTM Calib]

Yup, sounds like a de-laminating pcb

[Ken T]

Is the chip a BGA, eg with contacts underneath ?. If so its poss that some of the soldered joints have failed. You need to reflow it to remake the contacts.
MarkDTM knows how  

Ken

[Martin_1962]

Jumpered it - will take pictures!!

How do I reflow then?

[Ken T]

Basically you have to apply some flux and heat the whole board up to about 216deg C for about 90secs, to let the solder melt and reflow and remake the joint. There is a whole lot of stuff to find out, first is it leaded(Proper) solder or lead free ?. The temp above are for lead free, for Proper solder you only need to reach about 180deg. It is possible to do this in a toaster oven, http://www.instructables.com/id/Toaster-Oven-Reflow-Soldering-BGA/ but the proper way involves techniques like this http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=13241&mc=4 . There is always a danger that you might ruin the thing completely, I tried reflowing the Northbridge chip on an HP laptop motherboard using a cheap chinese (crap)  machine, and the BGA developed blisters !. This is known as "popcorning" in the trade; to you and me it means its stuffed!

Ken

[Marks DTM Calib]

Pop-corniing.

This is where moisture has got into the chip (whilst its been fitted to the board).......when you heat it up it expands and causes the case to pop....hence pop corning. And hence why new IC's are stored in vac pack bags with desicant and often in a nitrogen rich environment!

If we have to re-work boards in such ways, they are placed in an oven at just over 100degC for 24 hours in order to slowly dry the devices.......then they are re-re-flowed. You have to do the same to some new chips if thier bags are damaged or have been left open for more than an hour or so.

I suspect what martin is finding is that the via through the PCB have cracked. Sometimes you can fix these by inserting then tinned wire through them and soldering top and bottom. There are no BGA's on these boards from memory.

Ow yes, I now have evidence of lead free solder being more reliable if used correctly just to dispel that common myth  

[Martin_1962]

Now guess where one end of this is - that is correct under the chip

I had to repair the battery holder too.

Currently sitting in a jiffy bag waiting to have the holder refitted, and the last switch finished (araldited due to missing track), and a jump wire needs fitting to it.

Lizzys full rebuild is now second worst repair I have done.

And I am using up my handrail wire at a scarey pace!

[Ken T]

Pop-corniing.

This is where moisture has got into the chip (whilst its been fitted to the board).......when you heat it up it expands and causes the case to pop....hence pop corning. And hence why new IC's are stored in vac pack bags with desicant and often in a nitrogen rich environment!

If we have to re-work boards in such ways, they are placed in an oven at just over 100degC for 24 hours in order to slowly dry the devices.......then they are re-re-flowed. You have to do the same to some new chips if thier bags are damaged or have been left open for more than an hour or so.

I suspect what martin is finding is that the via through the PCB have cracked. Sometimes you can fix these by inserting then tinned wire through them and soldering top and bottom. There are no BGA's on these boards from memory.

Ow yes, I now have evidence of lead free solder being more reliable if used correctly just to dispel that common myth  

I think you hit the nail on the head with this statement. When we changed over to the leadfree stuff, people kept using components designed for use with leaded. THe humble DC socket on a laptop relies on the solder flowing well thro the PTH and filletting the joint on both sides to give mechanical strength to hold it in position. In other words the solder is providing a contact AND securing the component. Leadfree solder doesn't wick up the PTH to the same extent (to any extent?) and so DC sockets fail early. There are several examples of products made around the changeover period that suffered noticable failure rates compared to earlier products.

Hey, I don't mind, it keeps me in business repairing things, I can go "Oh dear, lead free solder again, sorry missus thats going to be expensive!".

Ken

[Welung666]

I can go "Oh dear, lead free solder again, sorry missus thats going to be expensive!".

After sucking copious amounts of air through your teeth