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Dan Collins · 05-04-2010, 23:14

If you can control the temp in the range 217 to 230, then it is best to leave the new BGA as is. The extra 2 thermal cycles of reballing with leaded is too risky in my opinion. And, to get the unleaded balls off, you have to apply over 217C to the chip anyway. The PC board is much more forgiving. Lets hear some more opinions on this!

I have no problem with the lower heater and upper heater spacing achieving the desired profiles. Last thing we want is to ramp up too quickly or ramp down too slowly.

I do admit, the TC can be affected by the upper heater unless you use the reflectors, then you can control that much better. But that is why I use two TC's or just do visual liquidus. There is no way around some heater influence to the TC unless you use reflective tape on it and that is usually space prohibitive or doesn't hold. It is best to check when the solder becomes liquid and then look at the TC reading. That lets you know how far your TC is off.

One more suggestion is to just use the TC as a reference and watch the chip. When the chip starts to drops and aligns, you know it has reached liquidus. This is when it is important to note the drop temp and try not to go more than 10C above that. It should stay in that range for 45-60 seconds total. So turn off both heaters about 20-30 seconds after liquidus to allow a slow cool down from the peak temp. Then wait for the TC temp when that chip drop occurred and.then park and fan on. Then I put a metal shield in between the lower heater and the board to get a quick steady cooling. This way you are just using the TC as a reference and not for accuracy.

That reflow time, above 217C, is the most crucial time for the heater settings. The board too close to the heaters will slow down the cool down from the peak reflow temp. This is the part that is the most frustrating and takes the most patience to control. But once you got it, you have mastered the machine and repairs start working. At least it did for me.

This is not an easy machine to use. It requires a clear mind and multitasking abilities to control it properly. Now if we had better temperature control, it would be easier. What I mean by that is control the heaters like in a reflow oven. Up and down.

05-04-2010, 23:14	#66 (permalink)
Dan Collins Freak Poster Join Date: Jan 2007 Posts: 210 Member: 437621 Status: Offline Thanks Meter: 19	If you can control the temp in the range 217 to 230, then it is best to leave the new BGA as is. The extra 2 thermal cycles of reballing with leaded is too risky in my opinion. And, to get the unleaded balls off, you have to apply over 217C to the chip anyway. The PC board is much more forgiving. Lets hear some more opinions on this! I have no problem with the lower heater and upper heater spacing achieving the desired profiles. Last thing we want is to ramp up too quickly or ramp down too slowly. I do admit, the TC can be affected by the upper heater unless you use the reflectors, then you can control that much better. But that is why I use two TC's or just do visual liquidus. There is no way around some heater influence to the TC unless you use reflective tape on it and that is usually space prohibitive or doesn't hold. It is best to check when the solder becomes liquid and then look at the TC reading. That lets you know how far your TC is off. One more suggestion is to just use the TC as a reference and watch the chip. When the chip starts to drops and aligns, you know it has reached liquidus. This is when it is important to note the drop temp and try not to go more than 10C above that. It should stay in that range for 45-60 seconds total. So turn off both heaters about 20-30 seconds after liquidus to allow a slow cool down from the peak temp. Then wait for the TC temp when that chip drop occurred and.then park and fan on. Then I put a metal shield in between the lower heater and the board to get a quick steady cooling. This way you are just using the TC as a reference and not for accuracy. That reflow time, above 217C, is the most crucial time for the heater settings. The board too close to the heaters will slow down the cool down from the peak reflow temp. This is the part that is the most frustrating and takes the most patience to control. But once you got it, you have mastered the machine and repairs start working. At least it did for me. This is not an easy machine to use. It requires a clear mind and multitasking abilities to control it properly. Now if we had better temperature control, it would be easier. What I mean by that is control the heaters like in a reflow oven. Up and down.