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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Tim Flanagan

#14423

Need advice on fixturing a smt LED board | 3 September, 1998

I need advice for locating 23 Gull wing LED's (all in a straight line) in the x,y, and z axis for a SMT PCB. It is a Hewlett Packard LED (P/N HMLA-QH00-01). The application uses a CCD to detect the position of a ball which floats in a resevior for a volume measurement. The light from the LED's shine on the resevior and is absorbed by the ball. The CCD detects the absence of light and turns it into a volume measurement. From our last few lots of boards (done outside) it is critical that the 23 LED's are positioned in a straight line and are flat to the board-not to mention the intensity fluctuation of the LEDs. I am looking for suggestions on previous experiences on how to fix the position of the LED. I was thinking maybe having a board made up with 23 cups that align with each LED. This would fix the 3 postions of the LED's but may be suceptable to user error before the reflow. I was also thinking of a two part fixture. The first being a x-y locator that would go onto the panel before the Pick and place machine. Each hole would funnel the LED into the correct x-y position. Then a second fixture would put pressure in the z position. Would i use board material for the fixture or some other material? The dimensions of the board are 0.4" by 6.45". The pad sizes are 0.030" by 0.030. I do not have the gerber files (political) but do have the artwork. I plan on making the pads bigger for better solder flow and strength. The legs of the LED can be up to 0.005" below the body of the LED-this is why i need z pressure when i reflow. All your help would be greatly appreciated. Thank you, Tim Flanagan.

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Stefan W.

#14424

Re: Need advice on fixturing a smt LED board | 4 September, 1998

| I need advice for locating 23 Gull wing LED's (all in a straight line) in the x,y, and z axis for a SMT PCB. It is a Hewlett Packard LED (P/N HMLA-QH00-01). The application uses a CCD to detect the position of a ball which floats in a resevior for a volume measurement. The light from the LED's shine on the resevior and is absorbed by the ball. The CCD detects the absence of light and turns it into a volume measurement. From our last few lots of boards (done outside) it is critical that the 23 LED's are positioned in a straight line and are flat to the board-not to mention the intensity fluctuation of the LEDs. I am looking for suggestions on previous experiences on how to fix the position of the LED. I was thinking maybe having a board made up with 23 cups that align with each LED. This would fix the 3 postions of the LED's but may be suceptable to user error before the reflow. I was also thinking of a two part fixture. The first being a x-y locator that would go onto the panel before the Pick and place machine. Each hole would funnel the LED into the correct x-y position. Then a second fixture would put pressure in the z position. Would i use board material for the fixture or some other material? The dimensions of the board are 0.4" by 6.45". The pad sizes are 0.030" by 0.030. I do not have the gerber files (political) but do have the artwork. I plan on making the pads bigger for better solder flow and strength. The legs of the LED can be up to 0.005" below the body of the LED-this is why i need z pressure when i reflow. All your help would be greatly appreciated. Thank you, Tim Flanagan. We are using your suggested template for through hole LED's with success. The holes for the LED's are drilled precisely with a CNC machine and the template includes two pins with spacers for the registration holes of the board. Of course with the through hole LED's we have much more freedom moving the LED's with the template, than you will have with SMT. I assume you place the LED's with a Pick & Place machine and they should be already well pre-aligned when you put the template over the board.

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