FYS4260/FYS9260: Microsystems and Electronics Packaging and Interconnect. Production of Printed Circuit Boards

Transcription

1 FYS4260/FYS9260: Microsystems and Electronics Packaging and Interconnect Production of Printed Circuit Boards

2 Learning objectives Understand central design and production processes of PCBs Layout principles High frequency design Background literature: Halbo & Ohlckers Chapter 6 and 7 The HDI handbook Malestroem: The printed circuit handbook 6 th ed.

3 PCB production virtual tour How to make a 4-layer PCB Nice 32 min tour of how small volume 4-layer PCBs are produced. Follow tour and check against procudure outlined in lectures Link: FYS4260/FYS9260 Frode Strisland 3

4 How to construct PCBs that work Internal details of a two head, gantry style pick-and-place JUKI SMT machine. In the foreground are tape and reel feeders, then the (currently empty) conveyor belt for printed circuit boards, and in back are large parts in a tray. The gantry carries two pickup needles, flanking a camera (marked "do not touch" to avoid fingerprints on the lens). "Pick and place internals of surface mount machine" by Peripitus - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - FYS4260/FYS9260 Frode Strisland 4

5 Electronics designers' role in product development: Designers are key personnel in the development of electronic products, but is not the only player, and must work in intimate cooperation with: Sales, marketing and customers Subcontractors Production process experts Cost engineers Logistics and purchasing staff etc. And a product's success relies first of all on it's ability to meet end user needs! Vscan Pocket Ultrasound: Pocket-sized ultrasound that may transform the way physicians see their patients. Developed in Horten, Norway, by GE Vingmed.

6 CAD Electronics design Advanced PCB CAD tools a neccessity, e.g. CadStar Schematics Component Library Critical Parameters (Placement Constraints, Electromagnetic Compatibility, Thermal Limitations, etc) Automatic Routing Final Touch Manual Routing (Verification by Final Simulation and Back Annotation) You learn the game from the project work I will skip details in the lectures FYS4260/FYS9260 Frode Strisland 6

7 Electronics construction: If you expect problems - you have a chance to get it right! Know your target requirements specifications Target the Right Quality The right quality is rarely "the best available" Select the Best Suited Technology/Technologies Select the appropriate Components: Right Compromise between Performance, Reliability, Cost, etc. Design for Production Design for Testability Design for Repair FYS4260/FYS9260 Frode Strisland 7

8 PCB production virtual tour Large scale automated production FYS4260/FYS9260 Frode Strisland 8

9 Administrative issues Still some who has not submitted schematics or specifications. Both are overdue. Deadline for completing (and having approved) designs is March 29th. Use the workshop offered! Lecturing material: Will distribute material for PCB lectures. Home exercises: Will distribute some exercises. Solution proposal will follow. Coming lectures: Ceramic circuit boards, Metallization systems FYS4260/FYS9260 Frode Strisland 9

10 Automated Thru-Hole Component Mounting Fig. 7.5: Simplified process in the axial inserter: 1): Cutting the components from the tape 2): Lead bending 3) - 4): Insertion 5): Cut and clinch 6): Return to starting position.

11 Surface Mounting: Deposition of solder paste or adhesive Soldering by wave solder process or by reflow process Fig. 7.13: Application of adhesive for SMD mounting by: a): Screen printing b): Dispensing c): Pin transfer

12 Main industry level soldering techniques Reflow soldering Wave soldering FYS4260/FYS9260 Frode Strisland 12

13 Reflow Solder Process Print solder paste Mount components Dry solder paste Solder by heating to melting of paste

14 Solder Paste Consists of: Solder particles (~ 80 % by weight) Flux Solvents and additives to give good printing properties (rheology) Typical mesh count in screen: 80 per inch Area ratio: A o = a 2 /(a+b) 2 Paste volume deposited: V = V o A o t "Solder ball test" for quality of solder paste and solder process

15 Solder Paste, continued Fig. 7.17: Microphotograph of Multicore solder paste type Sn 62 RMA B 3. The designation means 62 % by weight of Sn, 35.7% Pb, 2%, Ag, 0.3% Sb, RMA flux, 75 µm average particle size, 85% metal content, viscosity centipoise.

16 Reflow soldering Heating of solder on a conveyer belt according to a prespecified temperature profile "Mark Reflow Oven" by Heller Industries Inc php. Licensed under CC BY-SA 3.0 via Wikimedia Commons - k5_1826_reflow_oven.jpg Example reflow temperature profile for eutectic lead solder "RSS Components of a Profile1" by Zithan - Own work. Licensed under Public Domain via Wikimedia Commons - svg FYS4260/FYS9260 Frode Strisland 16

17 Surface Mounting: Wave Solder Process Apply adhesive by dispenser, screen printing or pin transfer Cure by heat or UV Turn board Wave solder Double-wave soldering machine common for SMT Not all SMD components suitable for wave soldering

18 Wave Soldering principle Fluxing Pre-heating Soldering (Cleaning) Fig. 7.9: a): Principle of foam fluxer. b): Control system for density and level of the flux bath.

19 Wave Soldering principle (2) Fig. 7.10: a): Principle of wave soldering. b): The real shape of the wave.

20 "Double Wave" Wave Soldering Lambda wave Fig. 7.15: Double wave for SMD soldering. The first is a turbulent wave that wets, followed by a gentle lambda wave that removes superfluous solder.

21 Double Wave Soldering Temperature Profile Fig. 7.16: Temperature profile during wave soldering in a double wave machine.

22 Failure modes in Wave Soldering Fig. 7.14: a): Shadowing in SMD wave soldering. b): Solder bridging on fine pitch package.

23 Screen Printing Woven screen (stainless steel or polyester) with organic photosensitive layer, which is patterned with holes (mask). Metal stencil with etched or drilled openings. Polyester stencil with punched or drilled openings. Definition and accuracy depends on type, mesh count, thickness, tension, squeegee, speed, etc. Screen Printing is a complex craft!

24 Screen Printing, continued Off-contact for screen printing, contact for stencil. Two-step stencil for best definition. The most advanced printers are fully automatic with vision system for alignment.

25 PCB Design: Design for Manufacture Few layers Coarse pattern Standardisation Robust design (coarse tolerances) Orderly placement

26 PCB Design: Design for Manufacture Fig. 6.1.a: Proper component placement for hole- and surface mounted components FYS4260/FYS9260 Frode Strisland 26

27 Orderly Placement, continued Fig. 6.1.b: Proper component placement for hole- and surface mounted IC components

28 PCB Design, continued Important Guideline for "Robust Design": Circuits should function with large parameter tolerances: Design windows allowing for variations in component parameters. Process windows allowing for variations in each process step. Regulatory requirements on safety and EMC should be passed within the specified design and process windows.

29 Design of Hole and Surface Mounted PCBs: Design Parameters Minimum Dimensions: The conductor cross section areas and resistivity of the material determine maximum current capacity and thereby minimum dimensions. Current capacity is limited by excessive heating of the conductors and the PCB. Maximum allowed ohmic voltage drop along the conductor also determines minimum dimensions.

30 Design Parameters: DC Line Resistance: DC Line resistance: RR = ρρ LL tt bb = RR LL bb ρ Ωm for Cu foil ρ is resistivity of the conductor material (ohm m) L is conductor length b L t t is conductor thickness b is conductor width Current I Sheet Resistance [ohm/square]: R sq = ρ / t R = ρ/t R = R L b R = R sq L / b 18 um copper: R sq ~ 1 mω/sq 35 um copper: R sq ~ 0.5 mω/sq

31 Design Parameters: Minimum Dimensions Fig. 6.2: Current capacity and temperature increase in conductors on PCBs. The upper figure shows the temperature increase (labels on each curve) at different combinations of cross-sections and currents). The lower figure shows the conductor cross-section (along the x-axis) as a function of the conductor width for different Cu-layer thicknesses.