吃瓜tv

Map the skipped location before changing the setup

Record the component, pin, board side, panel position and travel direction. Determine whether the skip repeats at the same physical position, follows a particular component lot or appears randomly. Keep photographs and carrier identification with the record. An underside image without orientation loses useful evidence about shadowing and access.

Compare affected and unaffected boards from the same run. If a carrier or product variant changed, record that difference explicitly. A recurring skip at one trailing-edge position deserves a different investigation from an intermittent pattern that moves with a flux nozzle problem.

Check whether flux reaches the intended surfaces

Review the chosen flux, application arrangement and evidence of coverage at the affected connection. A blocked nozzle, unsuitable application pattern or carrier obstruction can leave a location differently prepared from the rest of the board. Do not infer coverage simply because the machine's flux reservoir was full.

Drying and preheat influence the state of the material when it reaches solder. TWI's guidance on skipped wave joints identifies flux condition and application as relevant contributors. Use the supplier's method for monitoring the particular flux; do not apply a dilution or specific-gravity rule from another chemistry without checking its instructions.

Wave contact-time geometry

Distinguish preheat from the solder-contact event

The product must arrive at the soldering stage in an appropriate thermal and material condition. Measure representative locations rather than relying only on heater settings. Copper distribution, component mass, carrier design and loading can create differences across the assembly.

A change that improves one cold connection can overexpose a smaller neighboring part. Review component limits and the complete route. The thermocouple-location guide provides a useful measurement planning method even though the final sensor arrangement must suit the wave or selective process rather than simply copy a reflow setup.

Inspect the actual contact path

For wave soldering, assess wave consistency, board/carrier position and whether the intended underside features can contact solder. For selective soldering, review nozzle approach, programmed location, clearances and the delivered solder flow. Equipment checks must follow the machine's procedures and be performed by appropriately trained staff.

An obstructing component or carrier wall can shadow a connection. A nominally correct machine setting cannot overcome an inaccessible physical path. Preserve the geometry and orientation in the investigation so design or tooling changes can be considered when adjusting the process alone would be ineffective.

Use contact-time arithmetic only as a first check

For a simplified continuous wave-contact path, time equals effective contact length divided by travel speed after converting the units. With a 20 mm effective contact length and 1.0 meter per minute speed, the geometric estimate is 1.2 seconds. Real wave shape, immersion and board motion determine the actual contact history.

The calculator does not apply to a stationary selective-solder dwell unless its motion genuinely matches the assumed model. It cannot recommend a contact time or establish that a skipped pad touched solder. Use a suitable process measurement to validate the contact behavior before adjusting exposure.

Evaluate a correction against other defects

Increasing contact or changing orientation can affect bridging, drainage, flux residue and component exposure. Review those outcomes along with skips. A successful trial should show that the intended location now forms an acceptable connection without creating a worse condition elsewhere.

For inaccessible features, a controlled carrier or design revision may be the appropriate preventive action. A one-off hand touch-up can correct a unit but does not validate the original automated route. Record the repair and keep the root-cause action open until evidence supports closure.

Prepare a useful supplier discussion

Provide the board and carrier drawings, marked skipped locations, process route, material identities, travel direction and available flux/preheat/contact observations. State whether the issue is repeatable and how many opportunities were inspected. Do not report a percentage without identifying whether the denominator is boards, joints or specific pins.

吃瓜tv can review the manufacturability and assembly scope from those records. For a new build, identify carrier constraints early through the PCB assembly process. That is more useful than copying a soldering temperature from a different board and treating it as a universal cure.

What should be checked when only one row skips?

First preserve the row position relative to travel and nearby bodies. Compare it with an unaffected row that has similar hole, lead and copper geometry. If the rows differ in shadowing or thermal connection, a single contact-time number cannot isolate the cause. Record flux application, actual preheat and the observed contact region before changing the conveyor. A trial should compare the same joints and detection method so the result answers the original question.

Trace a missed connection through travel, chemistry and access

Map the affected joints relative to travel direction, neighboring components and any pallet or fixture. A location pattern can help distinguish a broad material problem from a localized access or contact issue. Preserve the original observation before touch-up removes the evidence.

Establish how the effective contact region was measured. Conveyor speed and contact length produce a simple travel-time estimate, but a changing wave shape or obstruction can alter the actual exposure. The physical contact relevant to a joint may differ from the nominal machine dimension entered on a setup sheet.

Review flux condition and application with the measured thermal history. More time or temperature cannot reliably compensate for an unidentified surface or chemistry problem. Check the actual material identity, handling and process sequence instead of treating every skipped joint as insufficient heat.

Compare joints with different thermal connections and geometries. Plane connections, lead projection, hole clearance and orientation can affect the operation. A change that improves an easy row may leave a shadowed or high-mass region unresolved. Select representative locations for the trial rather than only the most accessible ones.

Record what changes and how the result is evaluated. If conveyor speed changes, review the consequences for the whole thermal/contact sequence. Avoid comparing outcomes with different sample sizes or inspection methods and calling the difference a measured yield improvement.

For manufacturing review, supply a marked assembly view, travel direction, fixture information, material requirements and the observed failure distribution. Include the acceptance basis and whether the task is a new build or an existing-process investigation. The worksheet is a compact part of that record, not a substitute for the full process evidence.