fastbike
Mechanical
- Jan 12, 2008
- 1
Looking for some advise for the following:
I've been asked to help solve a problem on an automated manufacturing line. I won't go into detail on the entire line, just the area of concern. The problem area consists of a .016" thick by 6" wide tin plated steel web in which surface mount electrical components and a solder/flux mix have been previously applied to the top of the web via a pick-and-place machine. The web then travels through a 5 ft. long IR oven consisting of 24 independantly controlled zones of IR lamps placed beneath the web. The web travels in an indexed fashion per part length, approx 8" per index. Each 8" segment has to go through a preheat stage which is below the solder melting point and then a short duration final heat stage to bring each segment up to melting point for only a few secounds then back down to avoid component damage.
The systems are in place to follow each segment through the oven and control the temp of each segment as it travels, via IR measurement, feedback and PWM control of each of the 24 lamp zones. The problem is in real time measurement of the web temp via IR sensors to provide acurately control. Since tin plated steel has a very low emissivity and the web is filled with slots and holes, and there are 24 IR lamps shining up through the web from below, it is almost impossible to seperate the IR radiation from the web, from the background radiation.
One possible idea a came up with is to try to put an IR sensor via an IR fiber optic link directly over one of the larger surface mount components. The hope would be that the black plastic casing of the component would have a high degree of emissivity and with the fiber placed close to and directly over the part, it would seperate the IR reading from the back ground radiation. I would also expect that the temp of the component would rise fairly slowly due to marginal heat transfer from the web until the solder melts and flows, at which time I would expect a spike in the temp rise rate, making it easier to detect the moment melting temp has been acheived.
What do you think, would there be enough IR radiation from such a small area? Are IR compatible fiber optics cost effective? I'm open to any and all cost effective solutions.
I've been asked to help solve a problem on an automated manufacturing line. I won't go into detail on the entire line, just the area of concern. The problem area consists of a .016" thick by 6" wide tin plated steel web in which surface mount electrical components and a solder/flux mix have been previously applied to the top of the web via a pick-and-place machine. The web then travels through a 5 ft. long IR oven consisting of 24 independantly controlled zones of IR lamps placed beneath the web. The web travels in an indexed fashion per part length, approx 8" per index. Each 8" segment has to go through a preheat stage which is below the solder melting point and then a short duration final heat stage to bring each segment up to melting point for only a few secounds then back down to avoid component damage.
The systems are in place to follow each segment through the oven and control the temp of each segment as it travels, via IR measurement, feedback and PWM control of each of the 24 lamp zones. The problem is in real time measurement of the web temp via IR sensors to provide acurately control. Since tin plated steel has a very low emissivity and the web is filled with slots and holes, and there are 24 IR lamps shining up through the web from below, it is almost impossible to seperate the IR radiation from the web, from the background radiation.
One possible idea a came up with is to try to put an IR sensor via an IR fiber optic link directly over one of the larger surface mount components. The hope would be that the black plastic casing of the component would have a high degree of emissivity and with the fiber placed close to and directly over the part, it would seperate the IR reading from the back ground radiation. I would also expect that the temp of the component would rise fairly slowly due to marginal heat transfer from the web until the solder melts and flows, at which time I would expect a spike in the temp rise rate, making it easier to detect the moment melting temp has been acheived.
What do you think, would there be enough IR radiation from such a small area? Are IR compatible fiber optics cost effective? I'm open to any and all cost effective solutions.
