Please note that JavaScript and style sheet are used in this website,
Due to unadaptability of the style sheet with the browser used in your computer, pages may not look as original.
Even in such a case, however, the contents can be used safely.
CHAPTER 1 SOLDERING GENERAL
1.4 Visual Check
1.4.1 Visual check of lead-type SMD
| A visual inspection is carried out to check the condition of the solder connection between the component and the wiring board. The method of checking varies depending on the package. The defects that can occur on lead-type SMD packages includes displacement, wicking, unsoldered connections, and shorting. These defects are checked for by means of visual observation and optical system equipment. The defects detected by a visual check are shown in table 1-4-1. |
| Item | Outline | Symptom | Cause |
| Displacement |
 |
Relative position of SMD pin and pad are displayed | · Low accuracy of mounting machine · Dimensional tolerance of component unsatisfied · SMD moved by vibration while transported · SMD moved by flux during reflow |
| Bridge (excessive solder) |
 |
Solder remains between adjacent pads or pins | · Too much solder. Solder paste shifted during printing · Bent pin of SMD · Incorrect or inaccurate dimensions of pad and resist. |
| Pin lifted from PWB surface |  |
Pin lifted from PWB surface and not soldered | · Dimension of flat part of pin (y) of SMD not as specified · Unmatching between above dimension and solder thickness · Low pressure of mounting machine to press component · Pin deformed by contact with other objects while SMD handled |
| Not enough wetting |  |
Solder not spread enough on pad and pin | · Small quantity of solder paste · Low soldering temperature · Pad and SMD pin not wetted with solder enough (due to oxidization) · Degradation of solder paste |
| Wicking |  |
Solder absorbed by upper portion of pin and not enough solder left on joint | · Pin temperature rises more quickly than that on pad on PWB to melting point of solder during reflow |
| Manhattan (tombstone) phenomenon |  |
Chip component stands upright during soldering | · Uneven reflow temperature · Uneven quantity of printed solder · Uneven pad dimension |
| Solder ball |  |
Solder ball around pad or SMD | · Displacement or blur of printed solder paste · Solder paste flowing out to unexpected location due to heating · Ultra minute powder in solder paste not eliminated |
| Flux residue |  |
Flux residue on surface of PWB after cleaning | · Insufficient cleaning · Incorrect cleaning conditions (cleaning method, solvent, temperature, time) |
Table 1-4-1. Particulars of Appearance Inspection
  |
© 1995-2008 NEC Electronics Corporation
