assembly of flexible circuits with lead-free solder alloy...

Downloaded from the SMART Group website Downloaded from the SMART Group website www.smartgroup.orgwww.smartgroup.orgpresentations from Process Technology Seminars held at Nepcon Epresentations from Process Technology Seminars held at Nepcon Electronics 2006lectronics 2006

Assembly of Flexible CircuitsAssembly of Flexible Circuitswith Leadwith Lead--Free Solder AlloyFree Solder Alloy

Bob Willisleadfreesoldering.com

Introduction to LeadIntroduction to Lead--Free Assembly Video ClipsFree Assembly Video ClipsComponentwww.bobwillis.co.uk/lead/videos/components.rm

Printed Boardswww.bobwillis.co.uk/lead/videos/pcb.rm

Solder Paste Printingwww.bobwillis.co.uk/lead/videos/pasteprinting.rm

Component Placementwww.bobwillis.co.uk/lead/videos/plaement.rm

Reflow Solderingwww.bobwillis.co.uk/lead/videos/reflow.rm

Wave Solderingwww.bobwillis.co.uk/lead/videos/wave.rm

Hand Solderingwww.bobwillis.co.uk/lead/videos/handsoldering.rm

Rework and Repairwww.bobwillis.co.uk/lead/videos/rework.rm

Inspectionwww.bobwillis.co.uk/lead/videos/inspection.rm

X-Ray Inspectionwww.bobwillis.co.uk/lead/videos/xray.rm

These files ar e all in RealPlayer for matThese files ar e all in RealPlayer for mat


Flexible Circuit ConstructionFlexible Circuit Construction

Base Material - 0.05mm Copper 18/18 um ESPANEXfrom Holders Technologies Liquid Solder Mask - MPR80 Amber - Nippon Steel

Solder Finishes –

Immersion Nickel/Gold - Aurotech, from AtotechImmersion Tin - Stannatech from AtotechImmersion Silver - S terling from MacDermidOSP - Glicoat SMD P2 from Shikoku

Assembly Process StagesAssembly Process StagesFlexible Circuits -Screen Printing -Solder Paste -Placement -Reflow –Profiling -Automatical Optical Inspection -X-ray inspection -Optical Inspection -Rework -Rework Materials –


Flexible Circuit ConstructionFlexible Circuit ConstructionWetting indicator str ips for solder

paste dot solder ability patter n

0402 chip component positions

SOT23 component positions

SOIC16 component positions

Land Gr id Arr ay 40 pin

Assembly Pallet for Flexible CircuitAssembly Pallet for Flexible Circuit

Thermal relief areas on the base of pallet to improve delta T during reflow. Also consider drain holes under the flex if using vapour phase for lead-free reflow.



Modified flex ible pallet with thicker recess in the areas of the circuits and solderability test s trips. Drain holes for fluid are positioned under the flex ible when using vapour phase reflow soldering

Pallet and Flex CircuitPallet and Flex Circuit

Paste being printed/re flowed in side this area of the pallet



Double sided flex ible circuit on assembly pallet. Fixed and sprung pallets location pins used for the flex ible. Protrusion of pins above the circuit was approx imately 0.010”


Circuits do li ft on the edge of the tooling holes which does not cause a problem during assembly. This may be due to the copper being relieved around the hole causing the flex film to distort when clamped.


Printing of LeadPrinting of Lead--Free Solder PasteFree Solder Paste

The 0.006” (150um) stencil was recessed on the base of the foil to allow for any protrusion of the pallet clips. The stencils was recessed by 0.003” .

Printing of LeadPrinting of Lead--Free Solder PasteFree Solder Paste

Printing of lead-free solder paste with a 0.006” (150um)stencil. Two different aperture sizes were used on three different component footprints. Specific design rules used on the solderability wetting strips. Recesses were placed around pin protrusions from the pallet.


Component Placement on Flexible CircuitComponent Placement on Flexible Circuit

Placement of components on 0402, SOT23 and SOIC16 paste deposits. LGA Land Grid Array to be used in the Lead-Free Experience.

Reflow Profile of Circuit on PalletReflow Profile of Circuit on Pallet


Reflow Profile of Circuit on PalletReflow Profile of Circuit on Pallet

Vapour Phase Reflow ProfileVapour Phase Reflow Profile


Reflow Oven ParametersReflow Oven ParametersZone Number: 1 2 3 4

Top Set points (deg C): 195 229 220 270Bottom Set points: 195 229 220 270Conveyor Speed 39.5 cm/minute

Product Name: Flexible CircuitProcess Window Name: Sn/Ag/CuOven Name: RO400FC

Example LeadExample Lead--Free JointsFree Joints

Sn/Ag/Cu solder joints after convection reflow in air. The paste alloy was Sn96/Ag3/Cu05. Its was a type 4 powder also being used on another rigid board des ign for 01005.


XX--Ray Examination of JointsRay Examination of Joints

Images show voiding due to the time in a liquid state. The speed of reflow and the time above liquidus temperature was related to the pallet mass.

Incomplete reflow of wetting indicators due to non relief of pallet under strips

LeadLead--Free PPM Flex ResultsFree PPM Flex Results

Results from 20 flex ible circuits


Rework of Flexible Circuits with LeadRework of Flexible Circuits with Lead--FreeFree

Rework joints with hot air pencilUse flux prior to reflowRemove and replace componentsSet-point on tool 340-360oCUse lead-free wire to set-up air pencil distance from joints for reflow

Removal of solder shorts with solder wickShorts purposely added to SOIC16 leads for testingSet-point on iron 380oC

No issues of delamination or pad lift on parts after two rework operations. Pad dimensions for the parts used could be reduced to improve use of the surface area but adhesion of the pads would be reduced. Modifications can be made, but only when this is really necessary.

Rework of Flexible Circuits with LeadRework of Flexible Circuits with Lead--FreeFree

Video clip showing the removal of SOT23 with lead-free alloy SnAgCu from the surface of a flex ible circuit. Flux is applied firs t to aid removal fol lowed but reflow with hot air pencil.


Next LeadNext Lead--Free Process TrialsFree Process Trials

Double sided reflow trialsMore complex components/smaller pitchThrough hole components, reduced pin lengthWave solder and reflow flexible circuitsTrials on solder levelled circuits with other finishesSensitivity of flex with liquid solder mask to moisture

To download the FREE 85page SMART Group Lead-Free

Experience Report go to

www.leadoutproject.com

LeadLead--Free Experience Free Experience 33


BGA ManufactureBGA Manufacture




LeadLead--Free ExperienceFree Experience44


Contact details:Contact details:

Bob WillisBob [email protected]@bobwillis.co.ukwww.leadfreesoldering.comwww.leadfreesoldering.comTel 01245 351502Tel 01245 351502Fax 01245 496123Fax 01245 4961232 Fourth Ave, Chelmsford2 Fourth Ave, ChelmsfordEssex CM1 4HA, EnglandEssex CM1 4HA, England

assembly of flexible circuits with lead-free solder alloy...

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