Graping is a phenomenon marked by the appearance of unreflowed solder particles on top of the

solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...

mass. The solder that is partially coalesced looks like a cluster of grapes which is where the phenomenon’s name is derived." Present and future solder technologies: how new powders, activator chemistries and epoxy fluxes are evolving for production use."
/ref>

Causes

Graping occurrence has continued to increase since it was first identified in 2006. The

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

of the flux decreases as the temperature of the reflow oven increases.

Lead-free The Restriction of Hazardous Substances Directive 2002/95/EC (RoHS 1), short for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment, was adopted in February 2003 by the European Unio ...

reflow soldering temperatures are higher which results in more graping. Graping is also caused by increased surface oxidation. The increased surface oxidation is the result of smaller printed paste deposit volumes that cause a diminished surface area to flux ratio of the solder particle resulting in flux exhaustion. While

solder paste Solder paste is used in the manufacture of printed circuit boards to connect surface mount components to pads on the board. It is also possible to solder through-hole pin in paste components by printing solder paste in and over the holes. The s ...

can be manufactured using any size range, there has been a move towards finer particle sizes, especially for fine feature stencil printing. Finer particle sizes places added pressure on the solder paste flux to remove surface oxides which leaves the outside of the joint not fully coalesced producing the irregular surface finish known as graping." Best Practices Reflow Profiling for Lead-Free SMT Assembly"
/ref>

Resolutions

The graping phenomenon can be resolved utilizing proper solder materials in addition to correct reflow profile settings. Solder powders are available that provide a tighter distribution range as well as a high oxidation barrier. This barrier not only improves the paste release from the stencil, but also provides an ideal surface area-to-volume ratio. These solder powder characteristics help to eliminate the graping phenomenon. Future solder paste flux formulations provide sufficient activity paired with re-oxidation mitigation capabilities. This pairing means that graping can be resolved as it occurs which is ideal for miniaturization processes. There are also steps to take when setting up your reflow profile to reduce the amount of heat exposure to the solder paste during the reflow process and prevent graping. * Opt for a ramp to peak profile as opposed to a soak profile. * Adjust the belt speed to decrease the total time in oven to a recommended ramp rate of 1 °C/second from ambient to peak. * Utilize a peak temperature ranging from 235°-240 °C. * Cut back the time above liquidus (TAL) to 40–60 seconds.Solder Reflow Profiling Tips - Graping
/ref>

References

{{Reflist Soldering defects