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pcb_make_paste_grid

Split a thermal pad’s solder-paste opening into a grid of smaller fills to control reflow coverage and prevent IC drift during soldering.

Instructions

Split a single pad's solder-paste opening into a grid of smaller fills. The classic use case is the central thermal pad on a QFN / DFN / QFP -- a full-area paste opening makes the IC "swim" sideways during reflow as the molten solder pool reduces friction. Splitting the opening into smaller squares totalling ~50-75% coverage gives the IC something to bond to while letting flux gases escape.

Standard datasheet recommendations:

QFN / DFN exposed pad: 50-75% coverage, 0.3-0.5 mm squares with ≥ 0.2 mm gap (≈ 15 mils / 8 mils)
QFP heat-spreader: 60-70% coverage
Large connector body pads: 60% is usually enough

ALWAYS consult the IC manufacturer's recommended stencil pattern before defaulting to this script -- some packages specify a star, diagonal, or windowpane pattern; this tool only does a regular grid.

Args: designator: Component reference designator, e.g. "U5". pad_name: Pad identifier on that component. For QFN / DFN exposed pads this is usually "0" or the largest-numbered pad. Check the footprint first. min_grid_size_mils: Starting grid block size, in mils. Bumped up in 5-mil steps if coverage % is below target. Default 15 mils (≈ 0.38 mm). min_gap_mils: Minimum spacing between grid blocks, in mils. Default 5 mils (≈ 0.13 mm). min_coverage_pct: Target paste coverage as a percentage of pad area, 0-100. Default 60. Iterates grid size upward until met.

Returns: Dict with {designator, pad_name, grid_x, grid_y, grid_size_mils, gap_x_mils, gap_y_mils, fills_placed, coverage_pct}. The existing full-area paste opening is suppressed via PasteMaskExpansion = -pad_dimension on the pad cache before the grid fills are laid down.

Input Schema

Name	Required	Description	Default
`pad_name`	Yes
`designator`	Yes
`min_gap_mils`	No
`min_coverage_pct`	No
`min_grid_size_mils`	No

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.6.1Oct 29, 2026

TDQS

A4.6/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations exist, so the description must carry the burden, and it does disclose key behavior: the existing full-area paste opening is suppressed via PasteMaskExpansion = -pad_dimension before fills are laid down, and grid size iterates upward in 5-mil steps until coverage is met. It doesn't mention permissions, failure modes, or reversibility, keeping it short of a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the core purpose, then a rationale, then datasheet guidance, then args/returns — a clean structure. The datasheet recommendation block is slightly long but earns its place by informing parameter choices.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with zero annotations, the description covers purpose, behavior (paste suppression), iteration, params, and returns are documented via the output schema. Missing only edge-case behavior (missing component/pad) and permission requirements.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, so the description must compensate — and it does, documenting all five params with meaning, units, defaults, and iteration logic (e.g. min_grid_size_mils bumped in 5-mil steps, min_gap_mils default 5 mils ≈ 0.13mm, min_coverage_pct target driving iteration).

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb+resource: 'Split a single pad's solder-paste opening into a grid of smaller fills.' The QFN/DFN/QFP thermal-pad framing makes it immediately distinguishable from all the routing/via/teardrop siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit use case (central thermal pad, IC 'swimming' during reflow) plus a clear when-not caveat: 'ALWAYS consult the IC manufacturer's recommended stencil pattern... this tool only does a regular grid' for star/diagonal/windowpane specs. It also supplies numeric guidance (50-75% coverage, 0.3-0.5mm squares) that steers parameter choices.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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