Resolder (reflow) IC back to board

[ksrele]

Hello to all, I need help.

I just got used Wireless Logitech MX Performance mouse and it uses Unifying USB receiver but receiver just didn't work well. So I tried to open it to see what is the problem and then IC just fall of the PCB. Now I don't know how to solder it back...

I have cheep heat gun without temp control but it have two speeds, I tried to reflow IC with it and at first it look like I made it (it doesn't fall when I flip board) but when I just touch the IC it fals from board again. When I was heating the board I do it for about 2 mins and low speed. If I use higher speed IC is just blown away from board.

Board have elements on both sides so I'm afraid to put it in oven.

P.S. When I thought that IC is soldered back I tried to solder wires from USB cable to USB conntacts to try it but then IC fall again.

Sorry for my bad english.

[uncle_bob]

Hi

What does the other side of the IC look like?

Are you sure you can orient the IC so that pin 1 is in the right location?

Bob

[ksrele]

I forget to take a picture of bottom side of IC but it looks like this from this link: http://cdn2.bigcommerce.com/server1500/3b244/products/426562/images/418435/GE32SOT617-40__68114.1403717975.168.168.jpg

I know how to position it, i figure it out by hard way (with DMM) then i realise that there is a little dot in one corner on PCB and there is dot on IC in one corner .

[uncle_bob]

I forget to take a picture of bottom side of IC but it looks like this from this link: http://cdn2.bigcommerce.com/server1500/3b244/products/426562/images/418435/GE32SOT617-40__68114.1403717975.168.168.jpg

I know how to position it, i figure it out by hard way (with DMM) then i realise that there is a little dot in one corner on PCB and there is dot on IC in one corner .

Hi

My concern is that the IC should never ever fall off the PC board by it's self. There are only a very small number of reasons why it would:

1) There was something under the IC that pushed it off the board. That may show up in a picture of the IC.
2) The IC it's self shorted out and melted the solder. Again the IC would show signs of this.
3) The board it's self shorted out and melted the solder. The picture of the board shows no sign of this.

Of the three, number 2 is the best guess in your case. An IC that shorts out like this is 99.9% likely to be dead (sorry about that).

So how to solder it:

Wick the excess solder off the board and see how bad the solder is piled up on the IC. I'd bet there is plenty there. If so, flux the pads with a good liquid flux (use a tooth pick to dot it on).  Next slowly heat the board from the top with your hot air tool. The flux will boil off and then you should see the solder flow. The process should be done in under a minute. Let the board cool for at least 4 minutes before doing anything with it. If you don't see solder flow in a minute stop. You probably need more heat out of your hot air tool.

Bob

[ksrele]

Sorry I didn't have my camera to shot macro images - now I have it so this is how IC and board looks like close up.

I think that this USB receiver had rough life. It was trown and it was in dusty and worm places... previous owner didn't use it and didn't know how to save it. Then when he try to use it one day he figure out that it works for few minutes and then go off (bad solder under IC is my best gues) so he give it to me for free

So, now when I look at macro images I see solder under IC... How can I clean it? I think that board is clean.
Only problem is that I don't have liquid flux and nothing is working today so I can't buy it... I have some kind old flux pase, can I use that?

[ksrele]

And this is my hot air gun.

[Ian.M]

Totally sh!tty design FAIL:  QFN packages don't have enough contact area for reliable adhesion if the thermal pad isn't soldered to the board.  Also, one should *NEVER* rely on solder mask as a functional insulator, so even if the QFN thermal pad is isolated, the presence of both Vdd tracks and ground fill under the chip is asking for trouble.

[alsetalokin4017]

Yep. This is certainly very strange. All that solder on the thermal pad, but not on the corresponding area on the board, and solder mask acting as insulator.  And the chip looks like it's cracked anyway. This isn't going to end well -- especially using that hot-air blaster (more of a paint removing tool than a soldering tool.)

Old paste flux? Who knows what that might be, probably will turn out to be acid paste for plumbers.

My suggestion: Buy a new receiver, they are around 11-18 dollars US on Ebay.

[wraper]

Totally sh!tty design FAIL:  QFN packages don't have enough contact area for reliable adhesion if the thermal pad isn't soldered to the board.  Also, one should *NEVER* rely on solder mask as a functional insulator, so even if the QFN thermal pad is isolated, the presence of both Vdd tracks and ground fill under the chip is asking for trouble.

Race to the bottom. They were forced to to this to keep the design on 2 layers.

[Ian.M]

Still could have been done better - silkscreen over the Vdd tracks for a little more insulation and remove the solder mask over the ground fill in a line just inside the edge of the thermal pad to actually attach it.    Better yet, if room could be found to squeeze in Vdd vias outside the QFN outline (or use via in pad), get Vdd out from under and link it up on the other side, with a track under the crystal if there's no other choice.

Alternatively, use epoxy loaded with glass microspheres for spacing to bond the thermal pad to the board and provide guaranteed insulation thickness.

[ksrele]

Thank you guys for replies. I didn't do anythink more whit this receiver, I'm just waiting for good solution.

I don't know how to buy stuff from Ebay... I don't have internet pay card I have only Visa card that can be used only in my country (Serbia) and, I need to be honest here, I'm stupid when it comes to banks and cards and credit and all that. I know how to pay in cash and how to get cash from ATMs but I don't know how to pay online. Even bigger problem is that just recently we are granted PayPall in Serbia and many of us didn't use it before and now we just don't know how it works . And ebay didn't have option to ship stuff to Serbia, now I think that they do ship to world wide but I don't know how to pay

Now I feel embarrassed... 

Well... I think that I know what I'm going to do next. Tomorow, when IT shops starts working again I will go and buy Logitech K270 Keyboard. It is not so expensive (~30€) but it is pretty good keyboard and it uses the same Unifying receiver then I can use it with mouse too.

But, it will be so cool if I could fix this one.

I will try to buy tomorow liquid flux and try to reflow this again. Should I buy soldering paste to? Or I don't need it...
Can I use this heat gun or not?

[wraper]

You don't need anything more than soldering iron to solder it back actually. That heat gun is completely unsuitable for electronics. Just tin the pads of the IC, put it in the place with a decent amount of tacky or liquid flux. Then heat the pads around it with soldering iron, solder will melt and attach to the pads under the IC. But as already said, there probably is a crack in the IC so this might be useless.

[nanofrog]

There's a crack in it to my eyes as well, which is a clear sign it's dead. As you can't get the part, you'll have to buy a receiver and pair it as mentioned.

Wish it were better news.

[ksrele]

Now when you said it I can see crack on IC too...

Well, that is life... I got it for free what am I thinking? That it will be all OK? Not that lucky...  O0

OK, thank you all for trying to help me.

[Rasz]

the chip looks like it's cracked anyway

good clue as to how it came off the pcb, someone played soccer with it.

[Rasz]

someone played soccer with it.

No. It must be heat damage. The solder melted, not snapped from cold.

author already admitted 'fixing' it with a paint stripper

[jdraughn]

I once had a unifying receiver where the PCB broke in half (dropped the laptop while it was inserted). The PCB antenna broke off. I did manage to scrape the antenna trace on both ends and resolder it, and then use some hot glue to reinforce the joint, and it worked for a few weeks, but slowly the signal got worse and worse.

I had another logic receiver but it wasn't "unifying", even though it used the same chip. I figured it was just a matter of flashing the unifying firmware but gave up on that, so I used my hot air rework station to remove the unifying IC from the broken PCB and put it on the dongle that had the same chip, but different firmware.  It works like a charm. I didn't have any flux at the time and I didn't even both with adding fresh solder (was afraid of creating solder bridges).

[ksrele]

Wow, that is good story.   

I didn't take a good look at IC before I tired to solder it back so I don't know did I overheat the IC or that was the problem in the first place why it was not working OK and why it fall of the board when I just try to see what is wrong inside. I didn't pull it of PCB, it was lose already I just flip board and it falls to the ground. Maybe then it broke... I don't know.

But I have new information for you all: I just bought a brand new wireless keyboard with unifying receiver (Logitech K270) so I will able to use my "new" mouse.

I didn't say that I needed to replace micro switches on mouse because they were bad too... So this mouse had pretty rough life. 

[stmdude]

I didn't say that I needed to replace micro switches on mouse because they were bad too... So this mouse had pretty rough life. 

It's a damn good mouse. It been my favourite for quite a few years now, and I have several of them.

I'm currently test-driving the MX Master at work, and it _just_ might edge out my MX Performance mice. But I haven't decided yet.

[wraper]

I didn't say that I needed to replace micro switches on mouse because they were bad too... So this mouse had pretty rough life. 

It's just something wrong with those omron microswitches or how they are used, they die like cockroaches. I had new replacement G700 mouse sitting in the package for almost 2 years. When I took it out of the package for the first use, left switch was already bad (false double click). And I'm not somewhere in tropics with high temperature and moisture. First G700 started acting exactly the same way but it had some real use before that happened. My friend have the same issues with different logitech mouses. Maybe the current is not enough for contact wetting (IIRC 1mA is min current rating). Anyway, if logitech used both positions of SPDT switch for debouncing, this false double click issue would be virtually nonexistent. But they use it just as SPST switch instead.