First time SMD repair

[dieseltech82]

I have a customer that has a xuv that is missing on one cylinder. It was diagnosed with a bad ignition coil. So the coil was replaced and it went on its way. A short time later the xuv started to miss again. The tech removed the engine controller and opened it up. He asked me to look at it and I noticed there appeared to be a lot of heating at one of the ignition cool drivers. The engine controller is 900 USD so I called Digikey and ordered a couple of these drivers. This is my first time at attempting to des older a SMD component. I have basic tools, Hako knockoff soldering iron, copper wick, manual solder sucker,, flux and good silver bearing solder.  I was thinking about cutting the legs at the component to make removal a bit easier and then use the wick for the legs and pad. Anything else I should look for or be aware of? I do have a heat gun that would get hot enough to reflow solder but it's not as precise as the rework stations, so I don't know that I want to use that. Thanks.


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[tautech]

Sounds like you're on the right track however a couple of things to take care with.
Cutting pins should be done with care not to stress the pins and lift a pad, some use a craft knife, some a Dremel but you must also take care there's not hidden tracks under the IC that you might inadvertently damage.

Have you got an old PCB somewhere you can polish your skills on?

[dieseltech82]

I may have something lying around I can play with.


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[dieseltech82]

V5036s is the part number for the driver.


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[tautech]

V5036s is the part number for the driver.


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OK they'll be easy with side cutters on the leads and a hot iron in the tab.
The device might take some heat to melt the solder especially if it's that PB free muck. Don't be too hesitant to add additional solder to get better heat transfer from your iron and in no circumstances try to add force to move it.
When ready a light nudge with the iron should move it and then sweep or pick it from the pads.
Be sure to check your finished work for any solder bridges or tiny balls that may cause grief later.

If you are  to do the job any of the electronic service centers close by will handle it with ease.
It's a quite big SMD component....getting enough heat to the component will be the key.

[dieseltech82]

It looks big but is about the size of a dime. I'm pretty sure most of the solder on the tab has been vaporized by the component getting hot but I will definitely be sure to not use any force for removal. I'll take pictures of my progress tomorrow [emoji848]


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[tautech]

It looks big but is about the size of a dime. I'm pretty sure most of the solder on the tab has been vaporized by the component getting hot but I will definitely be sure to not use any force for removal. I'll take pictures of my progress tomorrow [emoji848]

This I doubt. ^^^
Assembly is such these days that very little solder is used and there may be no apparent solder fillet on the devices tab however some should be visible on the ends of the other 2 pins.
Like I suggested before additional solder will be necessary to help conduct the heat from your iron.

Looking forward to your report.

[dieseltech82]

The component is rated at 250 watts so it can get pretty hot I suppose. I'll try to take a good picture of the ones that are apparently good and the ones that aren't. Do you know if the solder pad covers the entirety of the component or just that tab on the right? The application engineer at Digikey though to would have a thermal transfer paste under the component. I suppose looking at the bottom of the new component will make it obvious [emoji23]


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[tautech]

The component is rated at 250 watts so it can get pretty hot I suppose. I'll try to take a good picture of the ones that are apparently good and the ones that aren't. Do you know if the solder pad covers the entirety of the component or just that tab on the right? The application engineer at Digikey though to would have a thermal transfer paste under the component. I suppose looking at the bottom of the new component will make it obvious [emoji23]

Pics are good. 
The pad will cover most of the underside of the component and the resultant solder connection transfers heat onto the pad where it's conducted away by traces and/or vias.
Solder becomes the *heat transfer paste* 

[Mr.B]

The application engineer at Digikey though to would have a thermal transfer paste under the component

In an SMD that size the only "thermal paste" will be solder.
I wonder who gave the person the title of application engineer?

As @tautech says, add more solder as you are trying to desolder the tab. It will help heat spread through the joint.

Start first with the small legs as tautech said.
What I do is add solder to the leg joint and while the iron is still applied, then cut the leg.
With the pad solder melted there is little chance of damaging the pad from the physical stress.
Don't spend too much time doing this or you will have a thermal stress problem with the pad... 

[tautech]

The application engineer at Digikey though to would have a thermal transfer paste under the component

In an SMD that size the only "thermal paste" will be solder.
I wonder who gave the person the title of application engineer?

As @tautech says, add more solder as you are trying to desolder the tab. It will help heat spread through the joint.

Start first with the small legs as tautech said.
What I do is add solder to the leg joint and while the iron is still applied, then cut the leg.
With the pad solder melted there is little chance of damaging the pad from the physical stress.
Don't spend too much time doing this or you will have a thermal stress problem with the pad... 

Good trick Mr.B, it makes perfect sense too especially if you're using Linesman sized side cutters. 

[Mr.B]

These...

[dieseltech82]

So you don't recommend using copper wick for the legs? I was planning on just using that to pull the solder away or is that only good on through joints? I was planning on using bolt cutters just like that [emoji106][emoji23]


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[Mr.B]

Use the copper wick to clean up the pads after you have removed the component.

[alsetalokin4017]

While I'm a great fan of using desoldering braid (copper wick) to remove through-hole components, it's not recommended for this application, because you will probably not be able to remove the thin layer between the legs and the pads using braid. And for sure it won't work to get the tab loose. Follow the heat-and-cut instructions above for the best results, and use the braid to clean up the pads after the old part is removed.

It's good that you bought three pieces of the replacement, because you should be prepared to find that the replacement overheats too. It's possible, or even likely, that the real circuit fault is somewhere else in the circuit. 

[dieseltech82]

I hope there isn't another issue [emoji17] I'm trying to save the customer from buying a $800 ECU. Not sure why an ECU for a gator is so much money other than its John Deere [emoji28]


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[dieseltech82]

Just finished the rework. Not too bad for my first time. I only had a small tip for my soldering iron, so I had to use my butane iron [emoji106] I'm sure several of you are shuddering right now.


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[krivx]

Looks like a good job.

[dieseltech82]

Looks like a good job.

Thank you


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[dieseltech82]

Here is a video of the coils firing after the repair. So far it's working [emoji106]


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[tautech]

Well done. 

From your pics I can see a trap for young players, that being the heavily stitched (vias) plane around the perimeter. That very likely *stole* most of your heat and made it necessary to use your little torch.
That's when a simple rework station with a fine nozzle really does the business.

Since we've seen the pics it's probable that a domestic heat gun, used carefully, could have done the job.

As you do more rework your basket of tricks grows. 

[jitter]

From your pics I can see a trap for young players, that being the heavily stitched (vias) plane around the perimeter. That very likely *stole* most of your heat and made it necessary to use your little torch.

I doubt it. The heatsink pad under the component doesn't connect to the heavily via stitched perimeter, there's quite a gap. And the pad itself has no via stitching whatsoever, so that little copper plane is all the heatsinking it gets. Pin no. 3 connects to a plane, but the pad has thermal reliefs to aid soldering.

In my experience, the big area of the tab is the real reason why desoldering a DPAK is not the easiest thing to do.

[tautech]

From your pics I can see a trap for young players, that being the heavily stitched (vias) plane around the perimeter. That very likely *stole* most of your heat and made it necessary to use your little torch.

I doubt it. The heatsink pad under the component doesn't connect to the heavily via stitched perimeter, there's quite a gap. And the pad itself has no via stitching whatsoever, so that little copper plane is all the heatsinking it gets.

Pin no. 3 connects to a plane, but the pad has thermal reliefs to aid soldering.

I get all that, the OP said he had too smaller tip and would have to have flooded the tab with solder that likely would bridge onto the stitched plane.
For those of us that have done a bit of rework we well understand the various problems but first timers need to experience these traps for themselves and lean.

Let's see what the OP comes back with for others to learn from too.

[dieseltech82]

The butane soldering iron I used is a Welller rebranded as a Snap On. I used a decent sized chisel tip, definately not the biggest one. The iron was able to get the pad hot enough to remove the component in 15-20 seconds I suppose. With more experience, it would probably be a lot quicker. I didn't use the largest chisel tip since I had to solder the legs too and I didn't feel like waiting for the iron to cool to change tips. I think I will try and invest in a better solder station or find a good used rework station. I don't do things like this often but it's nice to be able to repair something at a fraction of the cost of a new one.


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[nanofrog]

The butane soldering iron I used is a Welller rebranded as a Snap On

FWIW, you might want to check out Portasol, and see if their products remind you of above ^.