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Chat Area => General Discussion Area => Topic started by: Martin_1962 on 06 October 2008, 19:49:06

Title: Met my match SM PCB
Post by: Martin_1962 on 06 October 2008, 19:49:06
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?
Title: Re: Met my match SM PCB
Post by: TheBoy on 06 October 2008, 19:51:13
Inspect ssoldering with a decent magnifying glass.
Title: Re: Met my match SM PCB
Post by: Marks DTM Calib on 06 October 2008, 20:12:11
Pics!  :y
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 06 October 2008, 20:41:46
Will have to look for something digital with macro - but it is a keyfob
Title: Re: Met my match SM PCB
Post by: Taxi_Driver on 06 October 2008, 20:48:47
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.
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 06 October 2008, 21:40:46
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 :o
Title: Re: Met my match SM PCB
Post by: TheBoy on 06 October 2008, 21:46:22
Quote
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 :o
Have to sometimes take the rough with the smooth...
Title: Re: Met my match SM PCB
Post by: Marks DTM Calib on 06 October 2008, 22:00:31
Yup, sounds like a de-laminating pcb
Title: Re: Met my match SM PCB
Post by: Ken T on 06 October 2008, 22:52:52
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  ;) :y

Ken
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 06 October 2008, 23:11:02
Jumpered it - will take pictures!!

How do I reflow then?
Title: Re: Met my match SM PCB
Post by: Ken T on 06 October 2008, 23:35:28
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
Title: Re: Met my match SM PCB
Post by: Marks DTM Calib on 07 October 2008, 08:23:43
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  :y
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 07 October 2008, 08:56:41
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!
Title: Re: Met my match SM PCB
Post by: Ken T on 07 October 2008, 09:06:32
Quote
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  :y


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
Title: Re: Met my match SM PCB
Post by: Welung666 on 07 October 2008, 09:09:46
Quote
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  ;D
Title: Re: Met my match SM PCB
Post by: Marks DTM Calib on 07 October 2008, 09:21:03
Quote


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


Again, lead free solder will wick along a contact to the same extent as leaded (some types better!), its another lead free myth!

The problem as I have mentioned before is that lead free solder requires about an extra 15 degC to flow properly when compared to leaded. Trouble is that on some of the units on change over, they had a mix of components some of which would not tolerate the full extent of the required higher flow temp so a compromise was to run 5 degC or so below the optimum for a slightly longer period and the result is that the lead free solder does not flow so well.

Again, nothing to do with lead free solder which is excellent and evidence now sudgests, better, when used correctly.  :y

What you should be saying is 'ow dear, poor manufacturing procss again'  ;D
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 07 October 2008, 21:20:18
It works at last - been a nightmare though!

Hole drilled
(http://i91.photobucket.com/albums/k286/martinimber/kebfob/DSC02998.jpg)

(http://i91.photobucket.com/albums/k286/martinimber/kebfob/DSC02997.jpg)


Jumper wire
(http://i91.photobucket.com/albums/k286/martinimber/kebfob/DSC02999.jpg)

(http://i91.photobucket.com/albums/k286/martinimber/kebfob/DSC03000.jpg)

This replaces a ripped track
(http://i91.photobucket.com/albums/k286/martinimber/kebfob/DSC03001.jpg)
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 07 October 2008, 21:21:23
Last pic only attached one end

4th the hole soldered on is the faulty one
Title: Re: Met my match SM PCB
Post by: Entwood on 07 October 2008, 21:25:01
Thats all pretty small and accurate stuff ... :y :y :y

With my eyesight I wouldn't even see the hole you drilled !!!

Nice going ..  :y :y
Title: Re: Met my match SM PCB
Post by: Martin_1962 on 07 October 2008, 21:27:15
I am very short sighted so peep over the top of my glasses.

Not very safe though :-[

I use some of my modelling tools, pin chuck and a very small drill