Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


2 Hot 2 Handle

Views: 2144

#67879

2 Hot 2 Handle | 27 December, 2012

I've got an assembly I'll be building in a month or so. I'm at the profiling stage with a scrap, populated assembly on a durostone carrier. It's a complicated dog with a few thousand parts on it + 30 BGA's. It's a little over 0.100" thick. I've got 6 thermocouples under potentially problematic BGA's. As I approach the peak temps. I usually target (215C), the TAL goes through the roof (>100 sec.). If I keep TAL closer to where I like it to be, peaks are all low; around 200C to 205C. If I can't find a happy medium between TAL and PEAK, what should I consider doing?

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#67881

2 Hot 2 Handle | 27 December, 2012

From the temps you list, I'm going to assume you are using leaded solder. What type of oven profile are you using: Ramp-Spike or Ramp-Soak-Spike? I think you will have better results if you use the Ramp-Soak-Spike type of oven profile. Better chance of getting to your target peak temp while keeping your TAL lower. Use the first 3 zones to ramp up to about 170-175C. Use the next 2-3 zones to soak the board at 170-175. This allows the board and different thermal mass components to all come up to the same temperature evenly. Finally in the last 2 zones spike the temperature to reach your target peak temp.

Sounds like a very complicated board. Good luck!

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#67886

2 Hot 2 Handle | 28 December, 2012

I assume your problem is comming from the carrier. If it is so:

1. use carrier from another ,aterial 2. Use solder paste that handles faster profile

Good luck!

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#67887

2 Hot 2 Handle | 28 December, 2012

I assume your problem is comming from the carrier. If it is so:

1. use carrier from another material 2. Use solder paste that handles faster profile

Good luck!

reply »

#67892

2 Hot 2 Handle | 2 January, 2013

Thanks for the help. Ramp soak spike but due to the density of this assembly it's more like ramp spike. Yes, leaded. I'm getting similar results with or without the carrier. (I designed the carrier like swiss cheese, full of holes and scallops on the board edge to allow good air flow and minimize contact). It's just a big, fat assembly. I ended up running the first five zones just below the top end of soak then a 40 deg increase in zone 6 and a huge spike in zone 7. The density controls the slopes and they are easy on everything. Luckily our oven can handle a big differential in zone temps. My #'s now look really good except the thing doesn't cool down quick enough so my TAL is high. Not sure what to do as I'm maxing the cooling zones.

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#67982

2 Hot 2 Handle | 21 January, 2013

I had a similar situation with a very thick PCB (0.23") I could not get a TAL lower than 160 sec, I've spoken with my paste supplier about this issue and we have made some adjustments on the oven and we could lower it to 145 sec, I know it is higher than recommended by paste, but it was the best I could with such a thick PCB, we have not had any issue related to this in the last year, so I think we are soldering the right way.

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#68028

2 Hot 2 Handle | 28 January, 2013

Great, thanks. It's good to hear your assembly isn't giving you issues. We're stuck with the high TAL, too so I'll let you know what happens. We will be building inside of a month I think.

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