LED technology has signalled a small revolution for designers and manufacturers of electronics as well as for manufacturers of production resources. Simply by casting an eye over the products sold by any manufacturer of LEDs, we can get a real idea of the amount of applications which use this technology. Lighting, signage, heating, TV, medical applications….
This explosion of LED technology in the world of electronics design and manufacturing has brought with it changes in the way we execute and control the manufacturing of electronic circuits which have incorporated this technology. We are going to focus on two aspects in particular.
- Tight control achieved by LED binning.
LED binning is, basically, the classification of LEDs into groups, taking into account their colour, voltage (sometimes), and lumen.
Manufacturers of LEDs, due to the manufacturing process that is involved, are still unable to guarantee that 100% of the LEDs in a particular bin are 100% identical in terms of colour, voltage, and lumen.
This means that the same LEDs in different bins and in the same conditions, as a result of the current which circulates around the LED, shine with greater or lesser intensity. It therefore becomes necessary to correct this by using a resistance control.
Until recently, the only way electronics manufacturers could guarantee that all LEDs produced in the same batch belonged to the same bin was to divide the batches according to the number of different bins that the LED manufacturer or distributor supplied. This, as well as creating problems for FIFO and stock management, etc., also meant that it was necessary to have as many SMT assembly programmes as there were different possible combinations between LED bins and resistance.
It is true that certain clients in the automotive industry still require us to manufacture and deliver differentiated batches according to the LED bin; however, manufacturers of SMT assembly machinery are gradually beginning to develop applications which make it possible for the machines themselves to manage all of the possible combinations between LED bin and resistance in one single assembly programme.
- The challenge of managing and assembling the new LED formats.
One of the principles by which SMT has been governed from the beginning has been that the Pick and Place process parameters have been oriented or targeted towards formats of components with surfaces that are flat, solid and tough, generally made from epoxy or ceramic, such as capacitors, resistors, integrated circuits, etc.
But now new LED formats have exploded onto the scene. The upper surface of these LEDs is made from crystal, gel or soft silicone, and some are dome-shaped at the top.
This has meant that tools as well as process parameters have to cater specifically for these types of LEDs. Channelling the knowledge and know-how of the Pick and Place manufacturers that are essential for assembling these types of components at high speed, achieving the expected results, and without jeopardising the integrity of the LEDs.
There are some interesting articles at CREE containing advice about the correct handling of this type of LEDs. In one of these articles, the author draws on his experience to present us with a troubleshooting pyramid for these types of components, the base of which offers a solution (proper nozzle setup) which can solve up to 75% of problems. The pyramid offers solutions at each of its 4 levels, solving a progressively lower percentage of problems, until finally the solution at the top of the pyramid solves up to 5% of problems.
If we take a look at the vast portfolio of nozzles that have been created in partnership between OSRAM and SIPLACE, recommending a type of nozzle for each type of format of this type of LED, we can see that the pyramid makes perfect sense.
IKOR currently uses this LED technology with a gel or soft silicone surface, primarily in automotive lighting projects; in the course of our work, we have had to apply the actions described in this pyramid in order to produce products that comply with the expected quality and performance standards.