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STAKING OF LED FLEX-BOARDS TO A LAMP HOUSING

Introduction.

With the advancement of LED’s manufacturers have been looking to include them as part of the vehicle lighting system. What at first sight seems a straightforward assembly process it turns out to be anything but, the circuits require careful handling with each LED having its own individual heat sink needing to be firmly secured to the main housing.

Assembly and Method.

Typically a light housing consists of 50 plus LED’s connected together by a flex-board circuit with resistors and heat sinks attached, typically volumes are in excess of 150,000 lamp handed pairs p.a.

 
Early assemblies would screw the Heatsink / Flex-board in place, with 150,000 pairs requiring over fifteen million screws with expense, time and quality control it adds considerably to the overall finished lamp cost.

 
The solution is to mould and throw up individual stakes that can be processed in one simple 30 second operation capturing and recording all the process parameters.

 
Using the PHASA® Staking process it re-forms extensions to a moulding creating multiple fixtures simultaneously heating individual retention points and then with a separate action re-forms, clamping and chilling to a required head shape using pressure sprung loaded tools – essentially mimicking a “rivet type system”.

 
The process differentiates from others such as Ultrasonic with the possible danger to electronic circuits and problems of tool wear and noise when staking directly onto a metal surface. Hot Tool has stringing and tightness issues as well possible damage to the circuit by the extended hot tools.

The Flex-board

With careful handling the Flex-board is positioned onto a base moulding with multi points usually in a stepped pattern. Initial assembly is a manual operation with the circuit positioned and retained on the stakes for processing. At this stage it is advisable to create a slight interference fit to retain prior to process, this can be achieved by moulding an oversize square tapered pin to fit a round hole in the heat sink (fig. 1.) or add up-stands on a round peg (fig. 2.).

 
Stake Design for Interference fit on the Heat Sink


 

 
 When positioning the Heatsink and deciding where to put the stakes in relation on the moulding avoid overhanging an edge and position the stakes away from the unprotected flexible circuit.



 
Energy will be absorbed by the heat sink having an effect of increasing a cycle time and temperature input. The plastic circuit is quite tolerant of to heat applied but care needs to be exercised around any solder joints and adhesive melt. PHASA has undertaken process tests meeting manufactures specifications and can provide back up data results where required.

 
Resistors soldered to the flex-board are always best positioned away from the staked area and if possible on the non- processed area of the circuit as shown. When they are not grouped with an LED needing a heat sink a heat resistant material cover for additional protection is better used.

 
 
 
Once fully staked this sub-assembly is generally sealed within a main housing and becomes a non-serviceable item. It is important to have a repeatable process capturing confirmed assembly parameters and saving for future tractability.

 

The ongoing functioning of the LED’s, is very important and PHASA have developed a recordable guidance test system. Before staking a numerical powered value is taken against individual LED’s and compared once processed against a known range for a pass or fail.

 

 

PHASA have undertaken a number of successful LED / Flex-board Lamp projects and for a successful outcome it is recommenced to engage in early discussion with us for design considerations on your project.

 

 

To discuss your individual requirements call us on +44 (0)1638 561 478

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Phasa Limited
10 Victoria way
Studlands Ind Est
Newmarket
Suffolk
CB8 7SH
United Kingdom

Tel: +44 01638 561 478
Fax: +44 01638 667 310
Email:info@phasa.co.uk

© 2012 Phasa Limited All Rights Reserved.
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