Categories Lighting

LED Light Reparability

Think back some months, and picture the following scenario: ‘twas the night before Christmas, and suddenly an overhead LED light in the household went out. And so began a tale from the modern age…

The LED light in question illuminated the kitchen. No replacement was immediately available, as there is clearly no need to carry spares for a LED light that should last 50,000 hours (according to the marketing information on the box). And being after dusk on Christmas Eve the shops were shut so there was no hope of buying a replacement.

While some might consider stuffing a turkey by candlelight a romantic way to commence the festive season, reception of this suggestion matched the outside temperature in its ability to freeze mercury.  This called for drastic action…

LED lights are not generally sold on the basis of their reparability. But in this aspect some designs do have advantages over incandescent and florescent bulbs. With the old technology if a filament blew or the emissions mix became denuded, there was no hope of repair, at least not in your garage on a cold Christmas Eve. But some LED lights are constructed from packaged LEDs that are soldered to a printed circuit board. Usually the LEDs are wired in a string. This raises the driving voltage and increases the system efficiency. But if one LED fails then the entire lamp goes out. So, in theory, by identifying and replacing the defective LED, repair of the lamp should be possible.

Finding an open circuit LED in a string is easily accomplished, especially when the manufacturer has kindly provided a silkscreen marking on the PCB that indicates the polarity of each device. A replacement LED was fortunately to hand so the soldering iron was duly warmed and in a state of euphoria over the prospect of a turkey dinner and world peace, an attempt was made to de-solder the defective LED. Herein a minor difficulty was encountered. The solder refused to melt.

LEDs, for all their merits, are not as efficient as one might like in converting electrons into photons. The balance of the energy is liberated as heat. This heat has to be removed by conduction to keep the LED temperature within safe limits. FR4 is not up to the job so LED light manufacturers solder the LEDs to metal-in-board printed circuit boards. As the name suggests these have a metal core, which does the heavy lifting in terms or removing the heat and a dielectric skin that stops the copper tracks shorting to the metal core. The very best metal-in-board PCBs use a thin layer of nanoceramic for the insulator as this provides high dielectric potential while ensuring good transport of heat from the LED to the metal core of the PCB. So good are these materials at cooling the LEDs that a 15 Watt soldering iron is seriously underpowered for the task of de-soldering an LED.

Desperate times call for desperate measures. It can be officially confirmed that a Crème Brulee torch has just sufficient oomph to desolder a defective LED on a metal in board PCB, restoring light to the World, marital relations and the schedule for turkey dinner.

Could this be the start of a whole new industry with an LED light repair shop in every town?

Categories Blog

Enabling SSL Adoption Through Intuitive Interconnect…

From an interconnect standpoint, there are a wide and sometimes dizzying array of options available to the designer. Options are always good and there are a number of unique, SSL-targeted connector products that are optimized for different applications within a lighting system.  This month, we will discuss interconnection of the Chip On Board (COB) LED to facilitate easy integration of the light source into the lighting fixture or luminaire.

Chip-on-board devices began to enter the market a few years ago as manufacturers sought ways to increase light output beyond what was possible with single die devices. By tightly arraying die on a single, thermally conductive substrate and flooding the area with a phosphor pool, light output could be concentrated in a much smaller area than possible with discrete devices. This was not without issues since these substrates and their inherent thermal conductivity created challenges in how to effectively and repeatably solder a wire to pads located on a device that by its design was made to pull heat away from devices. Further complicating the COB is the wide variety of package sizes, solder pad locations, and plating types offered by manufacturers.  Given TE Connectivity’s (TE) long history and expertise in providing separable solutions to replace soldered connections, this clearly was a termination challenge and after some consideration, we decided there was an opportunity to offer a more effective solution to customers.

TE Connectivity sought to develop a highly adaptable, scalable holder to meet the interconnection needs for a majority of the COB products being introduced.  The first step of the design process involved a rather lengthy identification and analysis of common commercially available COB LEDs.  The simplified results of this analysis yielded three common COB LED attributes.

  1. Rectangular geometry
    2. Centralized light emitting area
    3.     Diagonally opposed (+) & (-) contact

The TE solderless scalable holder that was developed as a result provides a stable, repeatable interconnect to the aforementioned COB devices while providing poke-in wire termination technology, allowing ample clearance around the light source for lensing, achieving a low profile and facilitating heat dissipation from the device.  The scalable design allows a lighting manufacturer to choose from a wide array of COB devices for adoption into the final fixture. As an added benefit, the scalable nature makes it easy for TE to offer a reference pad layout to COB manufacturers for future COB designs which, when utilized, ensures an available off-the-shelf solderless interconnect solution for the new COB when released.

As with many adoptions of new technologies, standards soon follow in an effort to accelerate mass adoption.  One standard being followed today is Zhaga.  The international Zhaga consortium is creating specifications that enable interchangeability of LED light sources made by different manufacturers thus simplifying LED implementation in general lighting applications.  TE developed an interconnect solution focused on providing a quick path to develop compliant products. The solderless Z50 LED holder, aligned to the Zhaga book 3 specifications, incorporates a number of unique attributes providing snap-in LED retention, poke-in wire connection, and compatibility with leading optics to support the integration of LED lighting components within the LED ecosystem.  This 50 mm diameter holder is available at a standard height and a 3.4 mm low profile version.  A smaller solderless Z32 LED holder,  built off the same design principle,  but in smaller form factor at 32 mm in diameter is also offered for smaller COB LEDs.

Next month we shall discuss in greater detail the options around interconnect of the LED lighting fixture itself and system configurations.