Mechanical Design

Physical dimensions and mechanical considerations for PCB layout and enclosure design.

Component Heights

Physical height reference for PCB layout and enclosure design.

Power Components

Component	Designator	Package	Height	Notes
LM2596S-ADJ	U2, U3, U4	TO-263-5	4.5mm	DC-DC converters
L7812CD2T-TR	U6	TO-263-2	4.5mm	+12V linear regulator
L7805ABD2T-TR	U7	TO-263-2	4.5mm	+5V linear regulator
CJ7912	U8	TO-252-3 (DPAK)	2.3mm	-12V linear regulator
CYA1265-100UH	L1, L2, L3	SMD 13.8x12.8mm	~6-7mm	Power inductors
63951-1	J6, J7, J8, J9	FASTON 250 THT	8.89mm	Power terminals
470uF 25V	C3, C11, C20-C21, C24-C25	D10xL10.2mm	10.2mm	Electrolytic (tallest)
470uF 16V	C4, C22, C23	D6.3xL7.7mm	7.7mm	Electrolytic
100uF 25V/50V	C5, C7, C9	D6.3xL7.7mm	7.7mm	Electrolytic

Height Profile

xychart-beta title "Component Height Profile" x-axis ["TO-252 (U8)", "TO-263 (U2-U7)", "Inductors (L1-L3)", "Small Caps", "FASTON (J6-J9)", "470uF 25V"] y-axis "Height (mm)" 0 --> 12 bar [2.3, 4.5, 6.5, 7.7, 8.89, 10.2]

PCB Design Implications

Tallest components: 470uF 25V electrolytic caps (10.2mm)
Second tallest: FASTON terminals J6-J9 (8.89mm)
Third tallest: Smaller electrolytics & inductors (7.7mm / ~6-7mm)
Total board height: ~12mm including PCB thickness (1.6mm)
Clearance: Keep space around TO-263 packages for thermal dissipation
CJ7912 advantage: Lower profile (2.3mm) allows flexible placement
FASTON placement: Position at board edge for cable access
Capacitor placement: Consider grouping tall caps for enclosure fit

PCB Dimensions

To be determined based on component placement.

Heatsink Design

Aluminum PCB Heatsink Concept

A cost-effective heatsink solution using JLCPCB's aluminum PCB service. The aluminum PCB acts as a custom-fit heatsink that sits on top of the voltage regulators (U6, U7, U8) and DC-DC converters (U2, U3, U4).

Design Approach

Cross-section view:

    Aluminum PCB (heatsink)
    ┌─────────────────────────────────────────────────────┐
    │░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░│
    └──┬──────────┬─────────────────┬─────────────────┬───┘
       │ Thermal  │                 │                 │
       │ Pad      │    (cutout)     │    (cutout)     │
    ┌──┴──┐    ┌──┴──┐           ┌──┴──┐           ┌──┴──┐
    │ IC  │    │ IC  │           │Cap  │           │Cap  │
    │ U6  │    │ U7  │           │     │           │     │
    └─────┘    └─────┘           └─────┘           └─────┘
    ════════════════════════════════════════════════════════
                        Main PCB

Key features:

Same outline as main PCB - Easy alignment and mounting
Cutouts for tall components - Electrolytics (10.2mm), inductors (6-7mm), FASTON terminals
Solid areas over ICs - TO-263 (4.5mm) and TO-252 (2.3mm) packages for heat transfer
Thermal gap pads - Fill the gap between IC top surface and aluminum PCB

Target Components for Cooling

Component	Designator	Package	Height	Heat Dissipation
L7812CD2T-TR	U6	TO-263-2	4.5mm	High (1.5V × 1.2A = 1.8W)
L7805ABD2T-TR	U7	TO-263-2	4.5mm	High (2.5V × 0.5A = 1.25W)
CJ7912	U8	TO-252-3	2.3mm	High (1.5V × 0.8A = 1.2W)
LM2596S-ADJ ×3	U2-U4	TO-263-5	4.5mm	Medium (switching losses)

Gap Calculation for Thermal Pads

The gap between IC package top and aluminum PCB bottom depends on:

Aluminum PCB thickness: ~1.6mm
Standoff/spacer height: TBD
IC package height: 2.3mm (TO-252) to 4.5mm (TO-263)

Recommended thermal pad thickness: 1mm - 2mm (get multi-thickness pack to test)

Thermal Gap Pad Selection

Thermal gap pads (サーマルパッド) provide thermal interface between ICs and the aluminum heatsink.

Required Specifications

Spec	Requirement
Thermal Conductivity	12+ W/m·K (higher = better)
Thickness	0.5mm - 2mm (measure gap)
Size	100×100mm (cut to fit)
Electrical	Non-conductive
Material	Silicone-based

Recommended Products

AliExpress (Budget, 2-4 week shipping):

Product	W/m·K	Size	Price	Link
24W/mK Thermal Pad	24	100×100mm	~$3	AliExpress
Upsiren 24W/mK	24	100×100mm	~$3	AliExpress
Rgeek 12.8W/mK	12.8	100×100mm	~$5	AliExpress

Amazon Japan (Fast delivery, 1-2 days):

Product	W/m·K	Size	Price	Link
OwlTree 3-pack	12.8	100×100mm (0.5/1/1.5mm)	~¥1,500	Amazon.co.jp
Thermalright	12.8	120×120mm	~¥1,000	Amazon.co.jp
17.3W Non-conductive	17.3	100×100mm	~¥1,500	Amazon.co.jp

Application Tips

Clean surfaces - Remove dust and oil from IC and aluminum PCB
Cut to size - Match IC package footprint (TO-263: ~10×9mm, TO-252: ~6.5×6mm)
Slight compression - Pads should be 10-20% compressed for optimal contact
No air gaps - Ensure pad fully covers IC thermal surface

Ordering Aluminum PCB from JLCPCB

Create edge cuts in KiCad matching main PCB outline
Add cutouts for tall components (capacitors, inductors, FASTON terminals)
Export Gerber files with edge cuts only (no circuit needed)
Order as aluminum PCB from JLCPCB
Select thickness based on thermal mass requirements

Detailed KiCad procedure to be added after prototype testing.

Enclosure Considerations

To be added.