| Problem |
Observations |
Causes |
Recommendations |
| Device not flat post placement.
If the device is easily seen to be tilted to the naked eye then it is probably not flat enough |
All devices tilted |
Pick head on pick and place machine not square in relation to board surface.
Pick up tip damaged or burred. |
Machine needs to be reset or pick tip replaced before production.
It is also worth checking to see what effect the tilt is having post reflow. Whilst poor placement is not ideal, it does not always cause problems post reflow.
|
| All of the devices tilted in the same direction relative to device orientation |
| Only one area of the board affected, devices placed in just this one area are tilted |
Larger boards may be susceptible to sagging in the centre if poorly supported. Components in centre of board will show no paste deformation (see appendix). Components towards edge of board may be tilted.
Board may be being deformed during placement if over-travel is set too high, this will be worse as position moves towards centre of board.
Board may not be flat. |
Check over-travel and board supports the may need to be reset or altered.
Check bare boards for flatness.
It is also worth checking to see what effect the tilt is having post reflow. Whilst poor placement is not ideal, it does not always cause problems post reflow. |
| Varies across board. One device in one position always looks bad. |
| Device is twisted or not in the correct position on the board. |
Visually the device does not have good registration, it may be twisted or apparently in the wrong position.
There may be some electrical rejects. |
Too much solder |
Check reduction on stencil, for a 0.150mm (0.006”) stencil thickness 25% global reduction is required (see appendix). |
| Poor substrate layout. Substrate layout does not meet recommendations, solder pads are too big or in the wrong place. |
Check gerber files and or measure substrate using measure-scope. Check results against application note. |
| Poor reflow conditions, the solder paste is not completely reflowing. |
Check reflow profile against manufacturers recommendations, especially peak and time above liquid. |
| Thermal gradient across DirectFET MOSFET, end to end. |
See recommendations for tilt. |
