Qi2 25W changes more than the number printed on a product box. The Wireless Power Consortium identifies Qi v2.2.1 as Qi2 25W, but a production-ready charger still depends on the complete electrical, magnetic, thermal and mechanical system. A weak decision in any one of those areas can reduce sustained power, create interoperability failures or force an enclosure change late in the project.
From a factory engineering point of view, the right time to use a Qi2 25W design checklist is before industrial design is frozen. A good-looking housing is not yet a charging system. We first need to know what the charger must do, which devices it must support, how it will be powered and what evidence the brand expects at approval.
This checklist is the conversation we want to have with an OEM customer at the beginning of a project.
1. Define the product claim before selecting hardware
Start by writing the exact market claim. “Fast wireless charging” is too vague for engineering and too risky for packaging. The project brief should state whether the product is intended to be Qi Certified, which Qi profile is targeted and whether 25W is a peak operating point or a performance that must be sustained under defined conditions.
The WPC makes an important distinction between a certified product and wording such as “Qi compatible.” A professional buyer should be able to verify a certified model in the WPC product database. For an OEM program, the certification owner, brand name, model number and registration route should therefore be agreed before artwork is released.
We normally ask four questions:
- Which markets and sales channels will receive the product?
- Will the brand require its own listing and model identity?
- Is the design new, substantially similar to an existing product or based on a certified subsystem?
- Which claims will appear on the product, package and online listing?
These answers affect cost, documentation and schedule. They also prevent a common problem: engineering a charger first and discussing certification only after tooling.
2. Confirm the complete input-power path
A 25W wireless output does not mean a 25W adapter is sufficient. Conversion losses, control overhead and operating margin all sit between the input connector and the phone. The input source must support the voltage and current combinations required by the selected transmitter platform.
For a USB-C product, define the expected power adapter and cable instead of testing with whatever happens to be on the bench. Record the power-delivery profiles, connector temperature, cable voltage drop and behavior when a lower-power source is connected. The charger should fail gracefully or reduce power in a controlled way. It should not repeatedly start and stop because the input supply is operating at its limit.
The product specification should answer:
- Is an adapter included, optional or supplied by the end user?
- Which USB-C PD or other input profiles are supported?
- What is the minimum cable rating?
- How does the product indicate an unsuitable input source?
- What input protections are required for the intended environment?
Our TX and RX engineering workflow treats the adapter, cable, power stage and coil as one system. Testing only the transmitter board can hide issues that appear in the final retail configuration.
3. Freeze the magnetic and mechanical stack together
Magnetic alignment is central to Qi2, but magnets do not remove the need for mechanical tolerance control. Coil center position, magnet dimensions, ferrite, adhesive thickness, cover material, phone case and assembly variation all influence coupling.
The stack-up drawing should specify dimensions from stable datums. Do not dimension the coil only from a cosmetic edge that can shift after molding. Include the expected air gap and every material between the transmitter coil and receiver. Paint, decorative films and adhesive layers may look insignificant on a drawing, yet together they can change the working distance.
Before tooling approval, we recommend checking:
- Nominal and worst-case coil-to-surface distance
- Lateral and angular alignment tolerance
- Magnet polarity, retention and assembly poka-yoke
- Ferrite position and edge clearance
- Metal parts, fasteners or weights near the magnetic field
- Surface curvature and anti-slip behavior
- Phone-camera interference with the intended resting position
A mechanically complete sample is more valuable than a bare-board demonstration. The bare board shows that the electronics can transfer power. The full stack shows whether the product can do it repeatedly.
4. Build a realistic thermal budget
Wireless charging performance is temperature-dependent. A charger can reach a target briefly on an open bench and still reduce power after it is installed inside a compact housing. Ambient temperature, surface material, internal air volume, component placement and the phone’s own thermal control all influence the result.
We define thermal tests using conditions the product may actually see: room temperature, elevated ambient, different phone states, protective cases and extended charging duration. Temperature should be measured at the transmitter coil, switching devices, resonant components, connector and accessible surfaces. The test record should also show power over time. A single maximum-temperature number does not explain whether the system quietly derated after ten minutes.
Practical thermal work includes copper spreading, component placement, ferrite selection, controlled airflow where available and firmware thresholds. Adding a metal weight as a late thermal solution can create a new magnetic or FOD problem, so thermal and magnetic changes must be reviewed together.
5. Plan FOD calibration around the final product
Foreign object detection is not a value that should be copied from an evaluation board and forgotten. Housing material, coil construction, ferrite, magnets, nearby metal and assembly tolerances affect the transmitter’s loss model.
Calibration should be performed on representative assemblies. The validation plan needs both normal operating cases and defined foreign objects. We also test at different positions because a system can behave correctly at perfect alignment and differently near the edge of the charging area.
If a customer changes the top cover, magnet grade or internal metal structure after calibration, the change should trigger an engineering review. That is especially important when the change appears cosmetic to the purchasing team.
6. Design the validation matrix before samples arrive
Interoperability should not be reduced to “it charged our office phone.” Create a device matrix that represents the target market. Include current and earlier receiver generations, different sizes, common case conditions and the intended power adapters.
For each combination, record at least:
- Detection and charging-start behavior
- Alignment tolerance
- Negotiated and delivered power over time
- Surface and internal temperatures
- Restart behavior after repositioning
- Response to calls, camera use or other realistic loads
- Fault recovery and user indication
The WPC certification process provides formal compliance and interoperability work, but factory validation still matters. Certification samples and mass-production units must be controlled so that materials, firmware and assembly match the approved design.
7. Prepare for manufacturing variation
A design that works only at nominal values is not ready for production. Coil inductance, resonant capacitance, ferrite properties, adhesive thickness, magnet position and power components all have tolerances. The engineering team should identify which characteristics are critical to charging performance and convert them into incoming, in-process or end-of-line controls.
Typical controls include:
- Approved component manufacturers and revision-controlled BOM
- Coil inductance and resistance limits
- Magnet polarity and position checks
- PCBA functional test with traceable firmware version
- Charging-position and load test at end of line
- Golden sample and limit sample management
- Defined reaction plan for drift or substitution
This is where a factory contribution becomes visible. The goal is not merely to reproduce the prototype; it is to keep normal production variation inside a validated window.
8. Keep the certification unit identical to production intent
The WPC notes that coils, shielding and ICs by themselves are not Qi Certified products, and using components from another certified design does not automatically make a new product compliant. Housing, coil location, shielding and firmware can all affect performance.
That means the certification sample should be close to production intent. If the enclosure, connector, surface material or magnetic structure changes afterward, the team must determine whether additional testing or a different registration route is required. Keep a signed configuration record that links the tested samples to drawings, BOM, firmware and artwork.
What an OEM should send to the factory
To start efficiently, send the industrial-design files, target devices, charging claim, market list, input-power plan, preferred materials and the space available for the electronics. If the enclosure is not yet fixed, that is often an advantage. We can review coil position, thermal paths and service clearances while changes are still inexpensive.
You can review CowinLink’s wireless charging products and OEM modules for available starting points. For a new embedded or finished-product program, use the project enquiry page and include the target power, input source, product stack-up and expected annual volume.
Qi2 25W design checklist: final factory view
Qi2 25W development is most predictable when the mechanical, electrical, thermal, certification and production teams share one controlled specification. A transmitter board cannot compensate for an unsuitable magnetic stack, and a successful bench test cannot replace production controls.
Our preferred sequence is simple: define the claim, confirm the power path, freeze the magnetic stack, validate thermal and FOD behavior, test representative devices, then lock the production configuration. Following that order reduces late surprises and gives the brand evidence it can use when approving the product.
