NP560 suitability requires joint review of paste identity, material condition, printing transfer, and actual thermal history. Manufacturer profiles are trial starting points, not universal oven programs. If insufficient solder and voiding occur together, retain printing and post-solder evidence first. Determine separately whether volume was already insufficient before reflow, then choose material, stencil, or thermal-process adjustments.
First identify the specific NP560 supplied
Kester's public technical document dated 2021-10-20 identifies NP560 as no-clean, lead-free, halogen-free solder paste with ROM0 classification. Even with the same product name, confirm alloy, powder type, packaging, and lot. Low-voiding potential describes material-specific process behavior; it does not guarantee a void percentage on the current QFN center pad or eliminate cleanliness verification under every environment.
Retain package labels, manufacturing/expiry information, and applicable technical files at receipt. Typical viscosity values are comparable only with measurement methods, temperatures, and speeds. Unqualified shop-floor measurements cannot simply be subtracted from promotional values for acceptance. Review print release and melting conditions after powder-type or alloy substitutions; identical product names do not establish identical configurations.
Trace storage, warming, and line-side use
Manufacturer documentation distinguishes refrigerated shelf life for T3/T4 and T5 and requires warming to room temperature before use. Control actual lots according to their documents and packaging requirements, avoiding condensation from premature opening. Record warming start, opening, line introduction, stoppages, and leftover disposition separately. Keep original-container leftovers distinct from paste recovered from stencils. Supplier instructions and approved procedures determine whether recovery and mixing are permitted.
| Status Node | Record Requirement | Priority Actions During Exceptions |
|---|---|---|
| Inbound and Storage | Lot, powder type, expiry, and storage conditions | Verify deviation periods and material handling requirements |
| Solder-Paste Warm-Up and Opening | Time, environment, and packaging integrity | Prevent condensation; isolate first if data is insufficient |
| Solder Paste on the Stencil | Temperature/humidity, replenishment, pauses, and printing batches | Compare transfer stability and restart behavior |
| Excess and Scrap Materials | Source, quantity, status, and destination | Segregate using approved methods; avoid undocumented mixing |
From stencil aperture to actual paste volume
Paste behavior depends on more than squeegee speed. Aperture length/width, stencil thickness, walls, board support, separation, and cleaning affect release. Check whether defects cluster by aperture type, board position, or weak support before adjusting. If early printing is normal but degrades after long pauses, include pause/restart records rather than relying on shift averages.
Geometric example: a rectangular aperture is 0.40 mm long, 0.25 mm wide, and the stencil is 0.10 mm thick. Theoretical volume is 0.40×0.25×0.10＝0.010 mm³. If measured volume is 0.008 mm³, transfer efficiency on the same volume basis is 80%. This explains calculation only, not an NP560 acceptance limit. Keep SPI algorithms, board references, and calibration consistent when comparing parameter combinations.
Manufacturer printing guidance provides speed, pressure, and separation ranges, but optimum conditions vary by equipment and board. Fix stencils and support first in trials, starting with suitable pressure that clears the stencil surface. Record the observed object for every parameter change. Cleaners may interact with paste; release changes after switching stencil-wipe solvents are candidate causes too.
Use on-board curves to find mutually acceptable windows
NP560 documentation recommends peak temperatures of 235 to 255°C for SAC alloys and specifies calculating time above liquidus from the alloy used. This is a material-process starting point, not every component's allowable temperature. Actual profiling must satisfy component, PCB, and material limits together. Cover high- and low-thermal-mass areas, locations near hidden joints, and sensitive components rather than only easily accessible points.
Retain thermocouple attachment methods, measurement-point names, board configurations, and sampling methods. Oven-zone settings, conveyor speed, and on-board temperature are different data. Longer soaking may change voiding/tombstoning and increase component thermal exposure. Establish a shared window first, then compare controlled trials. Material files have revision dates; check applicability to the current lot without claiming they are the latest across every channel.
Branching diagnostic table for insufficient solder, bridging, and voiding
| Observed Result | What to Check First | Controlled Comparison |
|---|---|---|
| SPI shows local volume deficiency | Blocked apertures, release, board support, and material condition | Hold the profile fixed and compare trial-print volumes and distributions |
| Printing is normal, but post-solder center solder volume is abnormal | Via solder wicking, component lift-off, and thermal process | Corresponding aperture, via structure, and imaging results |
| Fine-Pitch Bridging | Misalignment, solder volume, collapse, and placement pressure | Distinguish bridges formed before and after reflow first |
| Voids Concentrated on Heat-Sink Pads | Windowpane apertures, gas escape, materials, and profiles | Change only factors that can be explained at once |
| Variation after long line stoppage | Line-side time, temperature and humidity, and recovery actions | Compare continuous printing and pause-recovery samples |
Retain original photos, SPI data, and board IDs before deciding on rework. Keeping only repaired passing boards removes evidence for testing hypotheses. Evaluate void locations, shapes, and thermal paths; one area percentage cannot judge every product. For related structural issues, see QFN thermal relief pads and printing.
How to form reusable conclusions from first-article testing
Method example: a power-control board has QFN voiding and insufficient solder on a few peripheral pads. Keep printing parameters fixed with the existing stencil and record peripheral/center volumes. If peripheral deposits are already insufficient, address release first. Once center volume is stable, compare two controlled thermal profiles within component limits, retaining board IDs, profiles, images, and load-temperature rise for each. Do not change paste, stencil, and oven speed together and attribute improvement to one factor.
Deliverable records include material lots/condition, stencil/aperture revisions, printing parameters, profiling files, defect statistics, and approved windows. State both sampled-board and inspected-pad counts, avoiding confusion between “a board has one defect” and “pad defect rate.” After first-article approval, production monitoring uses approved conditions. Reassess changes in powder type or PCB thermal structure.
supplementary issues in material usage
Does no-clean mean it can be directly coated?
Material names alone cannot decide this. Verify residue compatibility with coatings, later processes, and operating environments. Current product specifications define cleanliness or adhesion requirements.
Nitrogen Reflow Required?
Manufacturer information discusses air and nitrogen conditions. Determine nitrogen needs by comparing actual wetting, defects, and process stability, and identify them in quotations and process files rather than inferring them from material names.
How to maintain consistency through material and process comparison
When comparing old and new lots, confirm identical alloys, powder types, storage, and opened-container conditions, or explicitly identify these as trial factors. Keep SPI programs, datums, and calibration identical, and image the same objects under consistent analysis definitions. Separate center and peripheral pad statistics so large-area averages do not hide small-aperture abnormalities. Retain panel coordinates and support conditions for position effects. After parameter approval, record controlled factors and reconfirmation triggers such as stencil thickness, PCB finish, powder type, cleaner, and oven loading. Updating tables without programs may leave old conditions active. Reconcile leftovers, opening records, and waste destinations by lot; fresh paste additions cannot conceal unknown old-paste condition. After pilot production, organize retained samples and raw data, identifying rework, cleaning, and extra tests so future comparisons do not mistake different states for identical process results.
Source material and applicable scope
- Kester, “NP560 Solder Paste Technical Data Sheet”; version 2021-10-20; checked 2026-10-17; sections: product description, Process Guidelines, Reflow Process, Storage Handling and Shelf Life. Supports material identity and trial starting points, not a validated production window for current boards.
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