A thermal pad RFQ often begins with a nominal gap, but one number rarely describes the complete assembly. Mating surfaces can vary across their area, components can sit at different heights, and tolerance stack-up can change the space available after fastening. A useful gap map turns those observations into controlled inputs for supplier review without treating an early measurement as a guaranteed thermal result.
The goal is to show where contact is required, how the assembly is constrained, and how the measurements were obtained. The supplier can then discuss thickness candidates, compression behavior, sample options and validation questions for thermal silicone pads and related thermal silicone materials.
Define the interface before measuring
Identify both mating surfaces, the heat-source area and any electrically sensitive features. Mark the coordinate system, assembly orientation, fastener pattern and reference datums on a controlled drawing or model. If the interface includes several devices or raised regions, give each region a stable ID.
Explain what creates the final gap. Relevant factors may include board supports, component height, housing flatness, fastener seating, adhesive layers and nearby mechanical stops. State whether a pad is expected to fill a free space, accommodate local variation or also provide electrical isolation. These are review inputs, not proof that one material will satisfy every requirement.
Record the drawing revision, assembly revision and sample configuration used for the map. Measurements from an unfastened prototype should not be presented as though they represent a fully assembled production condition.
Build a practical measurement grid
Choose measurement locations that represent the whole contact region. A regular grid can work for a broad flat area, while device centers, corners, edges and known high or low points may be more useful for an irregular interface. Include enough points to reveal variation without implying precision beyond the method.
For each point, record:
- Point ID and coordinates or a marked drawing location.
- Measured gap and measurement units.
- Assembly condition, including fasteners and applied load where relevant.
- Tool or method used and its stated resolution.
- Part temperature and conditioning state if they materially affect the reading.
- Repeated readings or observed range when the result is not stable.
- Notes about obstruction, tilt, surface texture or uncertain access.
Keep raw observations as well as any calculated summary. A minimum, maximum and nominal value are useful, but they should not replace the location-level map.
Separate measured variation from tolerance stack-up
A prototype map describes the parts measured at that time. Production variation may also come from component height, board position, enclosure flatness, molded features and assembly force. List the controlled dimensions and their tolerances instead of silently adding a broad safety margin to the pad thickness.
Distinguish three inputs: actual measurements, drawing-based tolerance analysis and assumptions that still need confirmation. This helps reviewers see whether an extreme gap is observed, theoretically possible or merely estimated.
If several assemblies are available, keep their maps separate before combining the data. Label every unit and note whether it represents an intended production route. A single unusually high or low point should be investigated rather than automatically converted into a universal thickness requirement.
Describe the assembled compression condition
Pad thickness cannot be reviewed in isolation from the final assembly. Show the available space before and after fastening, the location of hard stops, the fastener sequence and any load-spreading plate. State whether the interface closes to a fixed dimension or depends on spring force and component compliance.
Avoid prescribing one compression percentage as a general rule. Appropriate compression depends on the selected material, thickness, surface condition, tolerance stack and mechanical limits of the components. Excessive force may affect a board, package, connector or housing, while insufficient contact may leave local gaps.
Ask the supplier to explain the proposed thickness range and the material data or sample work needed to review it. Final acceptance should be based on the project assembly and an agreed validation plan, not on gap mapping alone.
Include surface and contact-area information
Provide the dimensions of the intended pad footprint and identify keep-out zones, holes, ribs, screw bosses and sharp edges. Show whether the pad will bridge several devices or be divided into separate pieces. If the mating surfaces are stepped, curved or textured, include sections or photographs tied to the drawing revision.
Surface flatness and parallelism can affect local contact. Describe visible coatings, labels, protective films or residues that will remain during assembly. Do not assume that a larger pad automatically improves the interface; overhang, handling, tolerance and installation access also require review.
State how the pad will be located. Die-cut features, adhesive backing, carrier films or assembly fixtures can change the practical design. Any adhesive question should include the substrate, cleaning condition, installation method and expected service environment rather than a blanket bond-life request.
Define electrical and material questions separately
When electrical isolation matters, provide the applicable voltage context, required test method, construction constraints and system-level validation responsibility. Do not infer an approved isolation rating from thickness or thermal data alone. Material selection and documentation must be reviewed for the specific project, batch and target market.
Also describe operating and excursion temperatures, surrounding fluids, cleaning agents and expected contact conditions. Ask which evidence is available for the proposed material. Avoid converting a general datasheet value into a finished-assembly promise.
The gap map helps organize geometry. It does not guarantee thermal resistance, device temperature, dielectric performance or service life. Those outcomes depend on the complete stack, installation and test conditions.
Plan sample and validation stages
Use the initial map to identify candidate thicknesses or constructions for sample review. Label samples by material, thickness, lot and drawing revision. Record the installation procedure and inspect whether the pad stays positioned, contacts the intended regions and creates unacceptable mechanical interference.
Where appropriate, use pressure-indicating film, witness methods, dimensional checks or controlled disassembly observations to compare contact patterns. Each method has limitations and should be agreed before it becomes an acceptance criterion. Thermal testing should define sensors, load, ambient conditions, stabilization and comparison basis.
The Forvard Tech testing and quality control overview can help frame project-specific inspection and evidence questions. Supplier samples support review, but the buyer remains responsible for validating the completed assembly in its intended use.
Assemble the RFQ package
A clear thermal pad RFQ normally includes:
- Controlled assembly drawing, 3D model and section views.
- Marked interface zones and a coordinate-based gap map.
- Raw readings, method, tool, units and assembly condition.
- Relevant component, board and housing tolerances.
- Fastener pattern, hard stops and mechanical-force constraints.
- Pad footprint, keep-outs, placement and handling requirements.
- Thermal, electrical, environmental and documentation questions.
- Sample quantities, validation method and decision authority.
This package lets buyer and supplier discuss thickness candidates without hiding uncertainty or promising a thermal outcome. To request a project-specific review, submit the drawings, gap map, assembly condition, quantity stage and validation questions through the Forvard Tech RFQ form.