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SMT Solder Defect Causes and Fixes Reference Table

This table gives SMT and reflow engineers a quick lookup for the defects that appear on AOI and X-ray screens, with the causes to check first. Search by defect name or symptom, then export the table for your line troubleshooting binder.

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Defect	What you see	Typical causes	Usual detection	First corrective action
Tombstoning	Chip component stands on one end	Unbalanced paste volume, uneven pad heating, pad size mismatch, placement offset	AOI, visual	Check pad symmetry and stencil apertures, slow the ramp, verify placement offset
Solder bridging	Solder connects adjacent pads or leads	Excess paste, slumping, stencil underside smear, placement pressure, fine pitch aperture too large	AOI, X-ray for BGA, electrical test	Reduce aperture, increase wipe frequency, check paste viscosity and placement Z height
Insufficient solder	Small or incomplete fillet	Clogged aperture, low paste transfer, worn squeegee, poor board support	AOI, SPI upstream	Clean stencil, check area ratio, check print pressure and support pins
Excess solder	Convex ball of solder, hidden lead shape	Oversized aperture, stencil too thick, gasketing gap	AOI, SPI upstream	Review stencil thickness and aperture reduction, check gasketing
Solder balls	Small spheres beside the joint or under the part	Paste squeeze out, moisture in paste, fast preheat ramp, excess oxidation	Visual, AOI	Check paste age and storage, slow the preheat ramp, check placement force
Mid chip solder beads	One or two balls beside a chip body	Paste squeezed under the body, large pad overprint, high placement force	Visual, AOI	Use home plate or U shaped apertures, lower placement force
Head in pillow	BGA ball sits on paste but has not fused	Package warpage in reflow, oxidized balls, low paste volume, long soak	X-ray angled view, cross section, dye and pry	Review profile peak and time above liquidus, raise paste volume, check package warpage
Voiding	Gas pockets inside the joint on X-ray	Flux outgassing, large thermal pads, profile too fast, oxidized pads	X-ray	Segment thermal pad apertures, extend soak, consider vacuum reflow for critical parts
Non wetting	Solder does not adhere to pad or lead	Oxidized or contaminated surface, expired finish, insufficient heat, weak flux	Visual, AOI	Check surface finish age and storage, review peak temperature and flux activity
Dewetting	Solder pulls back leaving thin film	Contamination, finish defects, thin plating, repeated reflow	Visual	Check board lot and plating thickness, limit reflow and rework cycles
Cold or disturbed joint	Dull, grainy or rough surface	Insufficient heat, movement while solder cools, contamination	Visual, in circuit test	Confirm profile at the coldest joint, check conveyor vibration
Component shift	Part displaced from the pad outline	Placement error, vision calibration, conveyor shock, paste skid	AOI	Check fiducials, vision calibration and nozzle condition
Missing component	Pad pattern with no part	Pickup failure, feeder issue, part blown by convection, nozzle blocked	AOI	Check feeder pitch and nozzle vacuum, check airflow for small parts
Wrong polarity or orientation	Diode, IC or capacitor reversed	Reel loaded rotated, library rotation error, wrong centroid file rotation	AOI, first article review	Verify package rotation against datasheet and the machine library
Wrong part	Value or package differs from BOM	Wrong reel on feeder, mixed reels, BOM error	AOI, first article, LCR check	Enforce feeder to reel verification and barcode scan at setup
Billboarding	Chip rests on its side	Paste adhesion low, reel tape issue, high placement speed	AOI	Check tape pocket condition and placement settings
Lifted lead	Gullwing lead raised above pad	Lead coplanarity out of spec, uneven paste, warped board	AOI, visual	Check lead coplanarity on incoming parts and board warpage
Solder wicking	Solder climbs lead leaving a dry pad	Leads hotter than pads, fast heat rate, pad heat sink	AOI, visual	Soften the ramp and check bottom side heating
Graping	Paste partially coalesced, grainy surface	Paste exposed too long, insufficient flux activity, long soak	Visual, microscope	Shorten soak, check paste out time and flux
Flex or crack in ceramic capacitor	Crack under the termination, intermittent short	Board bending in depaneling, test or screwing, thermal shock	Cross section, insulation resistance, visual	Review depaneling method and board support, use soft termination parts where needed
Popcorning	Package cracks or delaminates in reflow	Moisture absorbed beyond floor life	Acoustic microscopy, cross section	Control floor life per J-STD-033 and bake exposed parts
Pad cratering	Laminate torn under the pad	Mechanical stress on brittle lead free laminates	Dye and pry, cross section	Reduce strain in handling and review laminate selection
Flux residue	Sticky or visible residue	Incomplete flux burnout, no clean misuse, insufficient wash	Visual, ionic contamination test	Check profile peak and wash process for the flux type
Solder splashing	Small solder spatter on the board surface	Wet paste, outgassing, fast heating	Visual	Check paste storage and preheat rate

This table lists typical causes that process engineers check first. Use IPC-A-610 for the acceptance criteria for your product class and always confirm the cause with data from your own line.

Defect data from your ERP

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How to use the table

Type the defect or symptom into the search box and read across the row: appearance, typical causes, usual detection method and the first corrective action. Work from the cheapest check to the most expensive. Printing issues are usually checked before profile changes, and profile changes before design changes. Export to Excel and add a column for your own line history so the table becomes a living troubleshooting record.

Where defects originate

Most SMT defects come from three areas: solder paste printing, component placement and the reflow profile. Industry experience commonly attributes a large share of defects to printing, which is why solder paste inspection after the printer is valuable. Design factors such as pad geometry, thermal mass imbalance and stencil design sit behind many repeat defects.

Print: aperture design, paste age, squeegee, support, underside wipe
Place: calibration, nozzle, feeder, library rotation, fiducials
Reflow: ramp, soak, time above liquidus, peak, cooling
Materials: surface finish age, moisture control, part coplanarity

Worked example

A line sees tombstoning on 0402 capacitors at one corner of the board. The table points to unbalanced paste or uneven heating. The engineer compares SPI volume on both pads, finds a consistent offset, and checks the stencil aperture and the oven airflow at that corner. Fixing the aperture offset solves most of the issue without touching the profile.

Common mistakes

Teams often change the oven profile first because it is easy to do on the screen. That hides the real cause and can create new defects. Another frequent mistake is treating all voids as failures; acceptance depends on the product class and customer criteria, not on a single fixed number. Record each change and its effect so the next shift does not repeat the experiment.

Frequently Asked Questions

What is the most common SMT defect?

It varies by line, but bridging, insufficient solder and tombstoning on small chips are frequent. Your own AOI Pareto is the right source. Rank defects by count and cost per board, then tackle the top two before touching anything else.

Is voiding always a reject?

No. Acceptance depends on the customer drawing, product class and the void location. IPC standards give guidance for certain features, but many OEMs set their own limits. Check your contract and drawing notes before scrapping boards.

Why does head in pillow only show on some boards?

Package warpage during reflow varies by part lot and board, so only some joints open up. Dynamic warpage, paste volume and ball oxidation together decide the outcome. X-ray with an angled view helps find it before field failure.

Should I change the profile or the stencil first?

Check the stencil and printing first in most cases, because paste volume drives many defects and a profile change affects every joint on the board. Use SPI data to confirm before changing anything in the oven.

If your AOI and SPI data already sits in an ERP or MES, Netray can help build a defect Pareto that ties escapes back to part, line and lot.

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