Project Prototyping. Slide 1

Transcription

1 Project Prototyping Slide 1

2 Project Prototypes Prototype Definition: Initial Electrically Functioning model of a product which demonstrates primary functions and modes Good prototypes should; Be constructed in a durable and portable fashion Facilitate requirement verification Enable demonstration of operating modes and features Be integrated from functional blocks of all team members Prototypes do NOT necessarily exhibit all facets of mass production design and construction Slide 2

3 Basic Prototype Methods Breadboard or Plugboard Advantages Solderless, Easy Mods Very Rapid Prototyping Well suited to TH 0.3 and 0.6 DIP IC s & Low Power Discretes Used in previous Labs Disadvantages Holes limited to #18-22 AWG solid leads/wires on 0.1 centers Circuit must be transported with extreme care Boards are subject to wearout, wire breakages, warping, etc Expensive, cumbersome for larger circuits Not suited to SMT, connectors, displays, power devices, switches, etc >10pF row-row capacitance Slide 3

4 Breadboard Circuit Slide 4 Image Source:

5 Breadboard Circuit Slide 5 Image Source:

6 Basic Prototype Methods Wirewrap or Termipoint Advantages Can be solderless or used in with solder Relatively Rapid Prototyping Well suited to DIP and SMT Conversions Easy Mods but Very Reliable Disadvantages All parts must fit into WW sockets/headers on 0.1 centers WW Wire is small, #30 AWG, <100mA, 250nH/ft WW Tool and special solid WW Wire required Best Results with Pre-stripped Wire Requires special WW sockets, bottom ID s and perf board Slide 6

7 Wirewrap Circuit Slide 7 Image Source:

8 Wirewrap Circuit Slide 8 Image Source:

9 Basic Prototype Methods Perfboard without Pads Advantages Used with top or bottom side solder wire-wire connections Can be used with DIP and SMT Conversion Sockets Mods possible but require unsoldering Reliable if used with hold down adhesives Disadvantages All parts must fit into sockets/headers on 0.1 center hole pattern Solder connections made with wire-wire or wire-pin Insulation on wire connections can be compromised with heat Slower than Wirewrap or solderless breadboard Requires higher degree of soldering skills Slide 9

10 Basic Prototype Methods Perfboard with Pads Advantages Used with top or bottom side solder wire-wire connections Can be used with DIP and SMT Conversion Sockets Mods possible but require unsoldering pads (vacuum required) Available with Gnd Planes, Power Traces/Busses Better solder connections than w/o pads, More Reliable Disadvantages All parts must fit into mountings on the hole pattern More expensive than std perfboard Slower than Wirewrap or solderless breadboard Requires moderate degree of soldering skills Slide 10

11 Perfboard with Pads The µtracer, a miniature Tube Curve Tracer / Tester Image Source: Slide 11

12 Perfboard with Pads Image Source: Slide 12

13 Perfboard with Pads Image Source: Slide 13

14 Basic Prototype Methods Deadbug Board Advantages Access to connection side of all parts Allows an excellent ground plane(s), Great for HF, VHF, UHF, RF Copper board can be scraped to provide power traces as well Inexpensive, Reliable if used with hold down adhesives Disadvantages Part markings are upside-down Not suited to digital or nodal intensive circuits Requires adhesive to deadbug parts Slow Method, Can be very delicate when part legs extend vertically Requires very high degree of soldering skills Slide 14

15 Deadbug Board Slide 15 Image Source:

18 Basic Prototype Methods CNC Routing Circuit Board Advantages Access to connection side of all parts Allows a single ground plane(s), Great for power supply, RF Can be std 62.5mil, 93mil, 125 mil or thicker board if needed Immediate Turn Around Disadvantages Limited to single and double sided boards Limited component density, thru-hole & 1st generation SMT Must use compatible CAD tool to generate artwork Slide 18

19 CNC Routing Circuit Board Slide 19 Image Source:

20 Basic Prototype Methods Printed Circuit Board PCB Outsourced Advantages Professional, repeatable performance for RLC, mass producible Can be used with or without component sockets, SMT or Thru Hole Parts Fast assembly once PCB is procured High current capability for any conductor By far the most reliable prototype method Circuit can be matched by computer to intended schematic Disadvantages Procurement Time of PCB Fab takes ~1-2 weeks, (quick turn is an option) Changes or mistake fixing can require unsoldering skills/tools Slide 20 Extra Design Task of Creating Board Layout File/Artwork

21 Printed Circuit Board PCB ExpressPCB - Full schematic capture and PCB layout Pad2Pad Custom PCBs - Layout package and ordering CadSoft EAGLE PCB Design Software Schematic and layout editor DesignSpark PCB - Schematic and layout editor Slide 21

22 Designing PCB 3 ICs: LM35 SO8, OP07 Dip 8 6 Capacitors: Ceramic Monolithic Axial 4 Resistors: 0.125W Axial Temp Sensor Circuit 10 Total Nodes Slide 22

23 Bill of Materials Example for Thermal Sensor Circuit Device Number U1 Mfg Part Number Description Qty Package LM35DCN Precision Temp Sensor 1 SO8 OP07CP Low Noise Bipolar OpAmp 2 DIP8 R1-4 10K, 1%, 1/4W Metal Film Res 4 Axial2 C uF, 50V, 20%, Ceramic Mono Capacitor 6 Axial2 U2,3 Slide 23

24 Circuit Layout PCB Board Slide 24

25 10 Guidelines 1. Make good power supply and ground connections A 30 AWG#, daisy-chained wire-wrap connection from chip to chip is very inadequate. For similar reasons to the decoupling, you must make low impedance power supply and ground returns. For single and double sided boards use 20mil or larger (wider) traces. For multilayer boards use separate planes for power(s) and ground(s) when possible Check ALL wire & trace gauges for proper current capacity. 2. Decouple ALL IC power inputs This includes analog, digital and data conversion IC s Employ a 0.1 uf ceramic capacitor from each supply to ground as close to the IC as possible. Switching internal to the IC can cause momentary voltage drops due to package and line length inductances. A local capacitor helps counteract this effect by providing local energy. Include separate bypass capacitors for both the positive and negative supplies Each circuit board should have additional bulk capacitors such as solid tantalum depending on local current draw Slide 25

26 10 Guidelines 3. Keep digital and analog circuitry physically separated if possible Digital switching, especially at microprocessor bus or video card speeds, can inject switching noise and other unwanted effects into analog circuitry. When possible use separate analog and digital power and ground return runs, planes and/or wiring back to a central point as close to the DC power source as possible. This will keep the digital noise out of the analog circuitry. 4. Assume you may need to make changes! Choose a suitable prototyping method that allow for changes, leave yourself enough space on your boards 5. Account for ALL your pins! Terminate all unused inputs in some fashion which allows them to be utilized if needed without substantial rework. For example, spare op-amps can be terminated by creating unity gain followers and grounding the input. Do NOT leave unused input floating unless the device is specifically designed for this condition. Slide 26

27 10 Guidelines 6. Make sure your parts are available before locking in your design 7. Construct in circuit blocks Construct and test functional blocks verifying performance as you go. Do NOT assemble more than a few blocks at a time before verifying functionality. The more circuits that are assembled and integrated, the harder it is to debug. Whenever powering up circuitry the first time, ALWAYS check the DC supply current as the circuit powers up with your hand on the ON/OFF switch. If there is a wiring or connection mistake, many times it shows up as an over current scenario. Be ready to turn off the supply in the event of an overcurrent. 8. Cleanliness of circuits is essential for low signal analog performance Don't use silicon sealant to tie down high-impedance or low current analog circuits! It may leave ionic laiden residue that can leak small currents which may be detrimental to circuit performance. 9. Use IC sockets on prototypes along with Thru-Hole technology if possible. The product design can be very different in its packaging technology. Do NOT assume you need to use the same IC packages in your prototype. 10. Treat the PCB and other interconnect systems as part of the circuit design. All PCB s, wiring, breadboards, etc have resistance, capacitance and inductance Slide 27

28 Soldering Best Practice ESD and heat protective lab bench top Heated Soldering tool (25W min iron) with small tip for electronic work Adequate ventilation Safety glasses and other protective clothing/equipment Small gauge #18AWG or smaller Sn63Pb37 rosin core solder wire De-soldering tool (wire braid or suction tool) Note: Some Solders Contain Lead Always Wash Hands After Contacting! Solder Pump Removal Tool Slide 28

29 Easy to see the difference between good-bad solder joints Good Solder Joint Bad (COLD) Solder Joints Slide 29

30 SMT to TH Adapters SMT IC s may need to be converted to ThruHole in order for prototyping Useful adapters are available as shown below; SOL16 to DIP16 Adapter PQFP44 to DIP44 Adapter PLCC20 to DIP20 Adapter TSSOP32 to DIP32 Adapter QFP80 to PGA80 Adapter SocketPLCC44 to DIP44 Adapter Slide 30

31 Plan the Project Prototype 1. Partition the Electronics, Determine # of Circuit Bds Considerations Annotated block diagram showing mapping of blocks to boards Functional Separations, Block Separations, Displays & User I/O Power Supply or Safety Circuits from Analog or Digital EMC and ESD protections, RF Circuits and Shielding Power and Heat Dissipation, Heat Sinks, Fans, Cooling Battery attachments and compartments Total path length and inductance from power source(s) Total surface area of components 2. For each design block, determine: Footprint area for or each unique part including mounting Total area of design block prototype parts Total area required for each circuit board (min 5X part area) Slide 31

32 Project Prototyping Plan 3. For each circuit board, select the type(s) of substrates & mfg Printed Circuit Board Outsourced Handmade Transfer Handmade Photo-Litho Pre-Perforated Boards Plastic, no pads, no busses Plastic, pads, no busses Plastic, pads, busses Flat Insulating Substrate Bread Board Other Slide 32

33 Project Prototyping Plan 4. Determine the type(s) of component attach Direct Solder or IC Socket Wirewrap Socket For Cu PCB or Perf Boards Adapters for SMT For Cu PCB or Perf Boards Deadbug Other Mechanical Slide 33

34 Project Prototyping Plan 5. Determine the type(s) of interconnection, tools required per board Solid Wire Solder Connection Use #18-22AWG for power Solder all connections Wirewrap #30 AWG For small signal connections Less than 25 ma No Soldering Necessary Slide 34

35 Project Prototyping Plan 6. Determine the type(s) of interboard connections Parallel or Buss Connections Power Connectors Ribbon Cable, Headers NEC, IEC320, DC, Molex Individual Signal Connectors Audio: RCA, Motorola Video, RF: BNC, F, N, S, SMA/B Telecom: Sub-D, RJ-11, RJ45, USB Slide 35

36 Project Prototyping Plan 7. Determine the overall enclosure types and numbers; Metal Enclosures (Provide Shielding, Grounding) Plastic Enclosures (Provide Durability, Workability, Impact Resistance, Insulation, Matched with Displays) Both are available in numerous off-the-shelf products Slide 36