Official Guidebolt Electrical Design Guide
Last Updated: 2021-03-22
Great electrical designers have a deep understanding of resistance, capacitance, inductance in the complex source-sink-impedance dynamics of signal-power transmission. Forward and return paths (ground shift), parasitics (leakage, distortion) and electromagnetics (EMI, EMC), form-tradeoffs (size/weight) and thermals (real-time distribution, ambient expansion, operating range, cycling, MTBF effects). Whiskering and corrosion (ECM, CAF), part-protection (SMT/THT shock-resist, IP rating, TVS, moisture-sensitivity, conformal-coat/encapsulation), user-safety (fuses, flammability, total-impact of material-lifecycle). Stack-up definition (layers, surface finish, impedance control), production stress (reflow conduction-paths, flux activation, soldermask-defined-pads), quality-assurance (optical inspection, QVL/PPAP), performance-limits and failure-modes (FIT, cascading-events). User experience (silkscreen, connector-mechanisms) and ease-of-maintenance (top vs bottom assembly, universal footprints/pinouts), modularity (universal interfaces, multiple firmware options).
Unit Standard: Metric. Dimensions are mostly mm and um.
Company-wide Lists: qualified vendor list (QVL), qualified parts list (QPL), shared symbol/footprint library.
Lifetime: 5 years MIN, 15 years TARGET MTBF
Safety: RoHS-compliant (RoHS3, EU Directive 2015/863, without exemptions), halogen-free (IEC 61249-2-21), red-phosphorous-free, antimony-free, REACH-compliant (U Regulation 1907/2006, without candidate substances).
Reliability: AEC-Q (target, grade 1), UL94-V0 flame resistance, glow-wire connectors, tin-finishes are matte-tin (reduced whiskering), operating temperature -40C to 85C MIN (-40C to 125C TARGET), MSL1 TARGET, MLCCs have soft-termination (bend-crack resistance), bulk capacitors are solid-material (ex. aluminum-polymer over aluminum-electrolytic for higher lifetime).
Usability: 1608 metric size TARGET (ease-of-assembly/repair), 4 mounting holes (square or rectangle pattern TARGET).
Ergonomics: rounded corners (major radius 5mm MIN).
Options: conformal-coating, encapsulation.
Fabrication Class: must be IPC-2 or IPC-3 for traditional fab.
Surface Finish: must be ENIG.
Soldermask Color: Green
Silkscreen Color: White
Electrical Testing: Yes
Impedance Control: Yes for high-frequency or analog PCBs.
Material: high thermal stability (ex. low-CTE, cycling tolerance, high electromechanical stability, high thermal conductivity (ex. 0.7W/mK is a good non-ceramic benchmark), good impedance-properties (ex. low relative-permittivity, low dissipation-factor).
Assembly: Must use lead-free solder. Preferred alloy is SAC305. Must use low-activity no-halogen (category L0) flux. Preferred flux is no-clean IPA-washable (good performance without cleaning but can be cleaned).
All pads must have rounded corners with radius 0.05mm MIN.
BGA footprint pads are generally recommended to be soldermask-defined.
SMT pads and reflow THT pads can be solid-connected to conductor-planes.
Easy-maintenance SMT pads and selective THT pads should have thermal-reliefs.
We prefer full-depth vias (normal plated-thru-hole, no blind or buried).
Vias-in-pad are good for space and thermals. We use them with exposed-pad-ICs when we have space.
Drill Dia, Annular Ring Dia Small: 0.2mm, 0.25mm (vias-in-pad standard) Compact: 0.25mm, 0.3mm (advanced-fab standard) Normal: 0.4mmm, 0.8mm (traditional-fab standard) 0.4/0.8 is the default via size in Kicad (popular). It requires a large-enough drill bit that breaks/wears less than smaller sizes (cost-effective). Easy: 0.5mm, 1.2mm (IPC-2221 Level-A)
board-edge to silkscreen, min 0.2mm
board-edge to external-layer-conductor, min 0.25mm
board-edge to internal-layer-conductor, min 0.5mm
board-edge to hole-edge, minimum 1mm
via-hole-edge to pad-edge spacing, minimum 0.2mm
via-hole-edge to via-hole-edge spacing, minimum 0.5mm
Footprints are spaced to support part-holding with tweezers (0.8mm tip-thickness).
Same-net pads can be closer together. Different-net pads should be further apart.
Attempt to have a reference-designator for each part-footprint.
Attempt to have a complete perimeter outline per part-footprint. In some cases a broken/dotted line is important for flux-scatter (ex. high-reliability BGA assembly).
Must have a functional-label per external-pin.
- Company Name (ex. Guidebolt)
- Part ID (ex. SOMEPART-MK1R3)
- Batch ID (ex. 2021-01-20_XYZFAB)
- MFG Origin (ex. Made in Canada with imported parts)
- flammability marker (ex. UL94V-0)
- WEEE directive marker
- UL Recognized
- UL Listed