Help with Surface mount

Thread Starter

Torbek

Joined Apr 19, 2019
36
Hey folks so I bought a batch of charger modules (tp5200 based) to charge two 26650's in series, and it seems every single one I have hooked up either fried straight away or fried after a couple of charge cycles. Anyway, I have, after reading the internet, decided to try replacing the IC itself, along with the flyback diode that might be poor quality on the original boards.

I have the IC's, but I am concerned about replacing. I have hot air, I have got some SMT solder paste, but no stencil....

Can anyone give me tips to get a good bond from the photo supplied?

1601037307850.png
 

Papabravo

Joined Feb 24, 2006
14,398
I urge you to take a closer look at identifying the reason for the failure. It might be tempting to conclude that low quality components are the root cause. If you replace the components and it does not fix the problem what would that tell you?
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
hmm yeah but I have all the parts now, not only that but it has worked for at least one other person!

It is odd and how these modules have passed QC is beyond me!
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
anyway, without a stencil I am concerned the IC's might not bed down properly. It's tiny and forcing it down will probably ensure it is not straight or with shorts so ideas would be appreciated, thanks.
 

SamR

Joined Mar 19, 2019
2,559
Use hot air to remove the components. Be very careful not to disturb close by components. Put down some paste and using an iron with small tip solder in the new part. Stencils are for new boards. If there is too much residual solder on the board use some wick with an iron to remove before placing new component. That board looks like it needs some. If new to you, try it on an old junk board first to get the hang of it.
 

jpanhalt

Joined Jan 18, 2008
10,221
You can buy stencils fro individual components, such as here: http://www.proto-advantage.com/store/

They are expensive and for a little bit more, you could make your own pattern with a lot of footprints on it and have it made.

However, for that component, I would not do that. First, I would clean up the pads with solderwick. Then, I would hand solder or use solder paste added sparingly. For something that big, my preference is hand soldering.
 

dl324

Joined Mar 30, 2015
11,487
I have the IC's, but I am concerned about replacing. I have hot air, I have got some SMT solder paste, but no stencil....

Can anyone give me tips to get a good bond from the photo supplied?
You can do it without a stencil, but soldering the connections on the bottom of the package can be problematic for DIYers.

Remove as much of the solder as you can before applying paste. If you use solder wick or a sucker, take care not to lift any pads.
clipimage.jpg
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
No chance using a soldering iron as the pads are barely visible on the actual package. They are mostly under it. My main concern is the heat pad and shorts. I guess sparingly does it
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
Well sorted, but limiting current to 200mA @ about 12v and heating becomes apparent. Like I said when these things work they work well properly terminating at 8.4v but unfortunately there must be a huge batch of faulty boards as every single one I have purchased has failed, and from different sources :-(

1601051053674.png
 

MrSoftware

Joined Oct 29, 2013
1,906
You can replace that chip multiple ways.

(1) Use air to remove the chip, slather the pads with flux, rub a solder wick over it to remove the solder, put more flux on the pads, place the chip and hold it down with tweezers, tin the tip of your iron and touch it to the tiny bit of pad that extends past the edges of the chip. The solder will suck under the chip. Use lots of flux and not too much solder. Flux will keep the solder watery and help prevent solder bridges.

(2) Use air to remove the chip, slather the pads with flux, make sure they are tinned lightly with solder, get the area warm with air, place the chip and finish heating until the solder flows. Carefully press the chip down with tweezers while you remove the air and let it cool.

You don't need solder paste for either method. Flux is your friend. Clean up with alcohol and a brush when you're done.
 

SamR

Joined Mar 19, 2019
2,559
The reason I like paste for SMD work is the liquid Kester 951 I use tends to evaporate quickly. 951 leaves a bit of white residue when dried up but less messy than paste or liquid Kester 186 so easier to clean the residue. Plus the paste tends to hold the SMD more or less in place when putting it on the board. YMMV
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
What is the chip's part number?
It's a TP5100 found here...

https://voltiq.ru/datasheets/TP5100-datashhet.pdf

Type tp5100 in to google you will see the modules. Someone has pointed out the missing 10uf caps on the switched side and I dismissed this but I am starting to question whether this might make a difference?

I had wondered if these chips were in fact rebadged TP5000 which were single cell only. However I have had a couple of charge cycles out of a couple of the chips and they charged the cells to 8.4v correctly!
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
You can replace that chip multiple ways.

(1) Use air to remove the chip, slather the pads with flux, rub a solder wick over it to remove the solder, put more flux on the pads, place the chip and hold it down with tweezers, tin the tip of your iron and touch it to the tiny bit of pad that extends past the edges of the chip. The solder will suck under the chip. Use lots of flux and not too much solder. Flux will keep the solder watery and help prevent solder bridges.

(2) Use air to remove the chip, slather the pads with flux, make sure they are tinned lightly with solder, get the area warm with air, place the chip and finish heating until the solder flows. Carefully press the chip down with tweezers while you remove the air and let it cool.

You don't need solder paste for either method. Flux is your friend. Clean up with alcohol and a brush when you're done.
Thanks, I will try that on another board then. It actually went quite well in the end just gentle heat not too much low air and it centralised itself and presented no shorts.

Ironically after the third board failure I let the chip heat itself up to the point I could remove it lol
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
So if anyone has any ideas... I have found another board but I would like to get to the bottom of this problem...
 

Thread Starter

Torbek

Joined Apr 19, 2019
36
Yeah I think they have all been faked. I am not sure it is even possible to get hold of the original from China full stop!
 
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