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Time and temp in lead and lead-free reflow

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#55699

Time and temp in lead and lead-free reflow | 25 July, 2008

I am trying to optimize my reflow profile. i have a 5 zone oven.

lead-free: for the 1st 3 zones, i am good, at about 150-200 deg for 150 seconds.

during the 4th zone, i am at a temp of 200-220 for 50 seconds.

during the 5th zone, i am at 220-245 for 50 seconds.

am i spending too much time between 200-220? will this affect the flux?

___ likewise, for leaded, zone 4 is 160-180 deg for 50 seconds before reflow in zone 5.

am i spending too much time between 160-180? ____

i can slow down alot and ramp up very slowly in the beginning. then try to stay in zone 5 for a long time. but this is bad for time and production. also, i am not sure if it is okay to stay at a lower temp for a long time (zone 1-4 would be pretty long).

or i can speed up and use zone 4 and 5 for reflow, but then my ramp up speed in zone 1 would have to be pretty high.

any thoughts?

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#55700

Time and temp in lead and lead-free reflow | 25 July, 2008

What paste are using? You should referance the manufactures time and temperature specification. Running lead-free in a 5 zone oven can be done with out a problem but it is not production friendly. If you are concerned with through put I would look for a 7 to 10 zone oven.

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#55703

Time and temp in lead and lead-free reflow | 26 July, 2008

I am not very concerned about production time, but it is always a thought! Quality is more importnant of course.

We have 2 different pastes, with almost identical requirements. We can get close to their profiles, but i am worried that i am spending a little too much time in zone 4 (or maybe zone 4 is about 10 deg too hot?) but it is the only way to get zone 5 up to temp.

i am looking for a trade off between best quality and reducing time if possible. if i have to slow down to half the speed, i will. but then i will be spending about 2 minutes just ramping up to 120 deg! not sure if this will pose another problem?

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#55717

Time and temp in lead and lead-free reflow | 28 July, 2008

Ideal situation is get a technical rep from the solder paste supplier. They know their paste better, and should be able to work out a profile based on their paste and your oven. Again, a technical rep, not the sales guy.

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#55724

Time and temp in lead and lead-free reflow | 28 July, 2008

Do you have a Slim-Kic? You can run a profile and then do predictions from there. Very useful tool.

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#55725

Time and temp in lead and lead-free reflow | 28 July, 2008

thanks, looks like an interesting product. any idea of the cost? they don't list it on their site. not sure if i can afford it yet.

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#55726

Time and temp in lead and lead-free reflow | 28 July, 2008

Take a look at this. Remember, these are only guidlines and can not replace any paste specs. As Real Chunks said, a profiler will be of HUGE help. We use this to determine what our top side temps are and to see if we have any problems with heat sensitive components. We are currently using the ECD mole, but the kics are pretty nice too. In my limited experience, depending on the number of layers, how many ounces of copper, number of boards on the array, your speeds/temps could change drastically. http://www.actel.com/documents/Solder_Reflow_LeadFree.pdf

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#55727

Time and temp in lead and lead-free reflow | 28 July, 2008

my oven has a built in profiler, it works fairly well, but it can not predict changes. my main concern was about the time right before reflow. i know that's where the flux is activated and i was worried that i may be spending too much time at the temp just before reflow and it might burn off the flux before it gets to work its magic!

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#55733

Time and temp in lead and lead-free reflow | 29 July, 2008

Oh, well if you can profile, model your profile to the profile supplied by the paste manufacturer. Anything outside of their recommended profile is all experimantal.

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#55734

Time and temp in lead and lead-free reflow | 29 July, 2008

Some profiles can be difficult to get exactly, so I was wondering what effect a slight deviation might have.

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#55745

Time and temp in lead and lead-free reflow | 29 July, 2008

Slight variations should have little impact on your product under normal conditions. All depends on your board.

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Leo

#55800

Time and temp in lead and lead-free reflow | 1 August, 2008

You can keep only the 5th zone as the reflow zone. And lower the first two zones to keep a good ramping rate. Meanwhile,please note the ting temperature in software or control panel is not the exact temperature in your PCB, you'd better get a KIC or Solderstart to run a profile and compare it with the solder paste manufacture's recommendation.

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#55808

Time and temp in lead and lead-free reflow | 2 August, 2008

Is there a limit to the time that most components can stay at temperatures around 130-200 deg c? if i slow the time, the first 4 zones will be at this temp for about 5 minutes in no lead process. i am concerned that some chips wont be rated at this temp for too long.

and i will eventually get a better profile system

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#55818

Time and temp in lead and lead-free reflow | 4 August, 2008

If you have concerns, you can look at the datasheet for each component or contact one of their application or materials engineers and find out what the components are rated for...process-wise. IE, how long can I be in the oven with this part, at what temperature, ramp rate rules, etc...This is also where one of those Kics or Moles, are very helpful. If I am not mistaken, I do believe there are some temp sensitive labels that you can buy to stick on parts or the board and they will let you know what temps you are hitting. I dont know where to find them but surely some one on this forum uses them and could give a part number for those. You could probably use that until you get the funds for a profiler.

Since the industry is going RoHS (YECH!)most parts will withstand temps up to 250*C-260*C(Peak)and more. Not all of them though...

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