# SMT Solder Defect Causes and Fixes Reference Table > Source: https://netray.co/tools/smt-solder-defect-causes-and-fixes-reference > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Look up tombstoning, bridging, head-in-pillow, voiding and other SMT defects with likely causes, detection method and first fix. ## Category electronics ## Industry Electronics Manufacturing ## Audience - PCBA process engineer - SMT line technician - Quality engineer ## Tool **Kind:** worksheet **Mode:** reference **Columns:** #### Defect **Key:** defect **Type:** text #### What you see **Key:** appearance **Type:** text #### Typical causes **Key:** causes **Type:** text #### Usual detection **Key:** detect **Type:** text #### First corrective action **Key:** first_fix **Type:** text **Rows:** **Defect:** Tombstoning **Appearance:** Chip component stands on one end **Causes:** Unbalanced paste volume, uneven pad heating, pad size mismatch, placement offset **Detect:** AOI, visual **First fix:** Check pad symmetry and stencil apertures, slow the ramp, verify placement offset **Defect:** Solder bridging **Appearance:** Solder connects adjacent pads or leads **Causes:** Excess paste, slumping, stencil underside smear, placement pressure, fine pitch aperture too large **Detect:** AOI, X-ray for BGA, electrical test **First fix:** Reduce aperture, increase wipe frequency, check paste viscosity and placement Z height **Defect:** Insufficient solder **Appearance:** Small or incomplete fillet **Causes:** Clogged aperture, low paste transfer, worn squeegee, poor board support **Detect:** AOI, SPI upstream **First fix:** Clean stencil, check area ratio, check print pressure and support pins **Defect:** Excess solder **Appearance:** Convex ball of solder, hidden lead shape **Causes:** Oversized aperture, stencil too thick, gasketing gap **Detect:** AOI, SPI upstream **First fix:** Review stencil thickness and aperture reduction, check gasketing **Defect:** Solder balls **Appearance:** Small spheres beside the joint or under the part **Causes:** Paste squeeze out, moisture in paste, fast preheat ramp, excess oxidation **Detect:** Visual, AOI **First fix:** Check paste age and storage, slow the preheat ramp, check placement force **Defect:** Mid chip solder beads **Appearance:** One or two balls beside a chip body **Causes:** Paste squeezed under the body, large pad overprint, high placement force **Detect:** Visual, AOI **First fix:** Use home plate or U shaped apertures, lower placement force **Defect:** Head in pillow **Appearance:** BGA ball sits on paste but has not fused **Causes:** Package warpage in reflow, oxidized balls, low paste volume, long soak **Detect:** X-ray angled view, cross section, dye and pry **First fix:** Review profile peak and time above liquidus, raise paste volume, check package warpage **Defect:** Voiding **Appearance:** Gas pockets inside the joint on X-ray **Causes:** Flux outgassing, large thermal pads, profile too fast, oxidized pads **Detect:** X-ray **First fix:** Segment thermal pad apertures, extend soak, consider vacuum reflow for critical parts **Defect:** Non wetting **Appearance:** Solder does not adhere to pad or lead **Causes:** Oxidized or contaminated surface, expired finish, insufficient heat, weak flux **Detect:** Visual, AOI **First fix:** Check surface finish age and storage, review peak temperature and flux activity **Defect:** Dewetting **Appearance:** Solder pulls back leaving thin film **Causes:** Contamination, finish defects, thin plating, repeated reflow **Detect:** Visual **First fix:** Check board lot and plating thickness, limit reflow and rework cycles **Defect:** Cold or disturbed joint **Appearance:** Dull, grainy or rough surface **Causes:** Insufficient heat, movement while solder cools, contamination **Detect:** Visual, in circuit test **First fix:** Confirm profile at the coldest joint, check conveyor vibration **Defect:** Component shift **Appearance:** Part displaced from the pad outline **Causes:** Placement error, vision calibration, conveyor shock, paste skid **Detect:** AOI **First fix:** Check fiducials, vision calibration and nozzle condition **Defect:** Missing component **Appearance:** Pad pattern with no part **Causes:** Pickup failure, feeder issue, part blown by convection, nozzle blocked **Detect:** AOI **First fix:** Check feeder pitch and nozzle vacuum, check airflow for small parts **Defect:** Wrong polarity or orientation **Appearance:** Diode, IC or capacitor reversed **Causes:** Reel loaded rotated, library rotation error, wrong centroid file rotation **Detect:** AOI, first article review **First fix:** Verify package rotation against datasheet and the machine library **Defect:** Wrong part **Appearance:** Value or package differs from BOM **Causes:** Wrong reel on feeder, mixed reels, BOM error **Detect:** AOI, first article, LCR check **First fix:** Enforce feeder to reel verification and barcode scan at setup **Defect:** Billboarding **Appearance:** Chip rests on its side **Causes:** Paste adhesion low, reel tape issue, high placement speed **Detect:** AOI **First fix:** Check tape pocket condition and placement settings **Defect:** Lifted lead **Appearance:** Gullwing lead raised above pad **Causes:** Lead coplanarity out of spec, uneven paste, warped board **Detect:** AOI, visual **First fix:** Check lead coplanarity on incoming parts and board warpage **Defect:** Solder wicking **Appearance:** Solder climbs lead leaving a dry pad **Causes:** Leads hotter than pads, fast heat rate, pad heat sink **Detect:** AOI, visual **First fix:** Soften the ramp and check bottom side heating **Defect:** Graping **Appearance:** Paste partially coalesced, grainy surface **Causes:** Paste exposed too long, insufficient flux activity, long soak **Detect:** Visual, microscope **First fix:** Shorten soak, check paste out time and flux **Defect:** Flex or crack in ceramic capacitor **Appearance:** Crack under the termination, intermittent short **Causes:** Board bending in depaneling, test or screwing, thermal shock **Detect:** Cross section, insulation resistance, visual **First fix:** Review depaneling method and board support, use soft termination parts where needed **Defect:** Popcorning **Appearance:** Package cracks or delaminates in reflow **Causes:** Moisture absorbed beyond floor life **Detect:** Acoustic microscopy, cross section **First fix:** Control floor life per J-STD-033 and bake exposed parts **Defect:** Pad cratering **Appearance:** Laminate torn under the pad **Causes:** Mechanical stress on brittle lead free laminates **Detect:** Dye and pry, cross section **First fix:** Reduce strain in handling and review laminate selection **Defect:** Flux residue **Appearance:** Sticky or visible residue **Causes:** Incomplete flux burnout, no clean misuse, insufficient wash **Detect:** Visual, ionic contamination test **First fix:** Check profile peak and wash process for the flux type **Defect:** Solder splashing **Appearance:** Small solder spatter on the board surface **Causes:** Wet paste, outgassing, fast heating **Detect:** Visual **First fix:** Check paste storage and preheat rate **Notes:** 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. ## Content **Intro:** 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. **Sections:** #### How to use the table **Body:** 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 **Body:** 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. **Bullets:** - 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 **Body:** 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 **Body:** 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. **Cta:** 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. **Faq:** #### What is the most common SMT defect? **Answer:** 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? **Answer:** 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? **Answer:** 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? **Answer:** 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. ## Search terms smt defects and causes, tombstoning causes, solder bridging causes, head in pillow defect, reflow soldering defects table, pcba defect troubleshooting, solder voiding causes, smt troubleshooting guide --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json