Printing vs. Dispensing Advances in Technology

Transcription

1 Printing vs. Dispensing Advances in Technology By Keith Bryant Chairman SMART Group Your Delegate Webinar Control Panel Open and close your panel Full screen view Submit text questions during or at the end

2 Printing vs. Dispensing Advances in Technology By Keith Bryant Chairman SMART Group Screen Printing is a 2000 year old technology The fundamental process and benefit s are unchanged today Simplicity Consistency Speed

3 Where are faults produced? 15% 15% 5% 65% Print Placement Reflow Component Machine Parameters Alignment System Squeegee Speed ( Type 4 Range mm p/s) Squeegee Pressure (Range 6.5 kg 9kg 320mm blade) Snap-Off Speed (slow 1mm p/s for 3mm) Temperature (refer to paste spec) PCB Support (preference)

4 Alignment Vision System Top Camera Capture Stencil Aperture Stencil Bottom Camera Capture PCB Fiducial or PAD PCB 1 PCB Conveyed and Clamped 2- Table align in X, Y and theta movement Precision Print Head Air Pressure replacing Springs Closed loop squeegee pressure control

5 Solder paste is characterised by the Ø and range of spheres Type μ Type 2 =75-53μ Type μ = 53-38μ Type μ Type 4 = 38-20μ Brand X FINE PITCH SOLDER PASTE 500g Tony Weldon Fine pitch printing - paste selection criteria Pitch / 0.635mm Paste type u Printing speed Alignment Manual / comparator Aperture design Stencil thickness 150u / 0.500mm u Suspended camera as min u / 0.400mm u auto 125u / 0.350mm / 0.300mm u Consult supplier auto auto u 100u CSP s Consult supplier auto u For recommended printing speeds always consult paste manufacturers specifications

6 Stencil and Paste Options Deposition on pads Type 75 microns Type 75 microns Type 100 microns Type 100 microns 5 Ball Wide rule Sufficient contact between the paste and the pcb pad relies on both the aperture width and the solder sphere diameters Solder sphere diameter 242 um Aperture width Example : Aperture width = 242 um (9.5 thou) Type 3 paste contains solder spheres of um since 5x 38 = 190um and 5x 50 = 250um it may be difficult to achieve a consistent 5 ball width Tony Weldon

7 A stencil is.. A sheet of metal with holes in it - used to deposit solder paste OR An Essential tool, the design and optimisation of which is critical to achieving consistent printed results and product quality Paste Roll Activation (PRA) MICRO FINE pattern on squeegee surface ensures paste roll and aperture fill to offer improved printed deposits

8 Aperture modifications for Pitched devices 10% O/ALL 5% O/ALL 5% WIDTH ONLY ORIGINAL PADS % REDUCTION 5% WIDTH & ROUND RECT 5% WIDTH & Oblong SPECIFIC REDUCTION Mid chip solder balls

9 Stencil Design Optimisation Original apertures Global Modification Wendy House Inverted Arrow Horseshoe Arrowhead Stencil Manufacturing Technology Precision Etching(Photo Chemical Machining) Accurate, Cost effective stencil solutions Used for component pitches down to 0.635mm Laser Cutting Improved dimensional accuracy for finer pitch requirements Used for component pitches down to 0.4mm Electroforming` Provides the best paste release of all the technologies Can be used for all components and packages Laser-formed Stencil material is electroformed and the apertures are lasered

10 Electroforming Process Conductive Mandrel Anode Basket Nickel pellets Photo-Resist Metal deposit A Typical Electroformed aperture profile

11 Optimised Paste Release for Finer Pitch Printing Would you choose the bucket or the drainpipe? Tony Weldon Stencil clogging Fine pitch printing 20-45u 200u

12 S t e n c i l t h i c k n e s s mm mm mm mm mm mm mm Stencil thickness calculator Single thickness stencils may only offer a compromise Glue 1.27 mm/pihr (0.050 ) mm (0.025 ) mm (0.020 ) mm (0.018 ) mm (0.016 ) mm/ 0201/CSP (0.012 ) Component pitch Stepped Stencils The etched pockets contain the finest pitch paste requirements Tony Weldon

13 When a Stepped Stencil is Not The Solution Advanced Dispense units inside the printer Advances in Tooling Laser Guided Features Manual tooling posts suitable for single and --double sided boards Quick programming via Gerber import utility Easy repeatable set up Two pin diameters (3mm and 10mm)

14 Other new stuff! To further improve print performance and better understand the behavior of flux-stencil interactions, two technology approaches are being studied: a Nano scale flux-repellent stencil coating and wetting the under stencil wipe with a solvent-based cleaning agent. Please see recent technical papers presented by Mike Bixenman of Kyzen Results of recent SMART on-line survey When encountering solder paste release issues when stencil printing fine pad features, what would be your approach? Reduce stencil thickness & maintain aperture size 51.4% Maintain stencil thickness & increase aperture size 8.6% Use solder paste with reduced particle size i.e increased type no. 28.6% Use alternative solder deposition techniques such as jet printing 2.9% Not encountered these problems 8.6%

15 Dispensing, an alternative technology or an add-on for screen printing Dot formation when dispensing Pulling a needle out of a pool of fluid will form a column that will eventually break into two or more pieces.

16 Dot Formation Factors that affect dot volume: *Needle dispense gap *Needle size *Dwell time *Retract speed *Material characteristics *Surface tension Common issues with solder paste dispensing are : Cold welding solder balls are crushed and clogged together Dripping Back pressure too high Foot in already dispensed paste wrong programming Needle contamination dispense gap too low / too high Broken needles incorrect dispense height Unstable quality temperature change The dispensing process is difficult and has a lot of parameters that influences the result! The dispensing process is also very slow!

17 Non-contact means Jetting Nozzle The energy for breaking the fluid from the dispense tip comes from fluid momentum not from surface tension to the substrate What is solder jet printing? Jet Print Head Depositing solder paste without stencils using inkjetting technology. Shooting droplets of solder paste whilst moving over the PCB Up to 1,800,000 dots/h

18 Jetting Advantages *Speed *No Z-axis motion *High flow rate -- up to 500 dots/second *No stopping between dots required jets on the fly *No needle backtracking to remove fluid stringing *No effects from substrate warping Jet Printing 3D deposits

19 Non-Contact Jetting Advantages in Production * Mechanical Dispensing * Requires needles to be cleaned * Stand off post wears * Stand off post tracks material over board Non-Contact Dispensing No problem with any pad layout No post to wear No post to clean Non-Contact Jetting Advantages in Production *No mechanical stand-off contact with boards reduces process development time *No under board support design or setup time Foot orientation ok Foot lands in previously dispensed material Foot lands on pad changing dispense gap

20 It works Like a print head *Fast changes of cartridges *Cartridge has ID chip *Selects machine settings *Prevents human errors *Enables a switch from leaded paste to leadfree or glue in seconds The print head

21 Jet Printing solder paste Optimized solder paste volumes Each solder joint can be optimized for: solder paste volume, position, height, shape, pad coverage

22 Jet Printing for higher quality Don t spend time on rework Optimise paste volume The key to good quality Each package/pad has its optimal volume requirement Screen printer Depending on stencil thickness, the same package will get completely different volumes on different boards Paste volume for 0.4mm QFP when using mm stencil Paste volume for 0.4mm QFP when using mm stencil Jet Printer Program solder paste volume / pad Repeatable process Jet printed deposit for 0.4mm QFP The volume is programmed individually and is repeatable

23 Jet Printing challenging boards and components Jet Printing as add-on technology Repair Board stretch and alignment Boards are aligned and any stretch is compensated for by using board fiducials Board warpage Laser height sensor maps board surface Control software ensures the the print head travels with constant jet height over the board

24 Optimize solder paste volume *Applying solder paste instead of dipping the top component creates a much more stable process.

25 Easy to edit paste deposits to fill via holes adjacent pads Jet Printing challenging components Pin-in-paste Top view Bottom view Build piles of solder paste After reflow, bottom view

26 Reballing BGA s BGA before reballing Jetted solder paste Magnification Jet Printing gives faster response times Software driven and stencil-free Fast set-ups Immediate changeovers On-the-spot revisions Minimum operator intervention Replaces screen printers or separates production into high mix and low mix lines

27 Conclusions 1 Screen Printing is fast and relativly low cost Technology is proven over many many years Recent advances are coping with most Technology Challenges Process Developement is still on-going Paste for this technology in low cost But stencils have a lead time and repeated fine tuning affects lead time and budgets. Conclusions 2 Jet printing gives you unlimited design opportunities. Jet printing can be used to replace a screen printer or as an add-on tool. It solves challenging applications. It is gaining momentum in the industry. Paste and consumables can be expensive It could be a great addition to a manufacturing site as it is NOT always a choice!!!!

28 The Bottom Line Both technologies have their strong points And there are limitations to both I love the flexibility of Jet Dispense to optimise production quality easily, but still have concerns about consumable costs and the need for programming skills For Prototype Houses Jet Dispense is great For volume production with fixed designs I would favour Printing but maybe with a jet dispense off line for repair, NPI and PIHR etc Thank You!