The soldering conditions (preheating temperature, soldering temperature and their durations) shall be within the limits in the catalogs or product specifications.
When the capacitors are used exceeding the limits given in the catalogs or product specifications, cracks may occur in the capacitors and the reliability may deteriorate, especially the rapid temperature changes and partial heating during soldering may cause cracks.
Generally recommended temperature conditions for reflow soldering is as follows:
NOTE Lead-free solder has a higher liquid phase temperature than eutectic solder (Sn-Pb).
Confirm the heat resistance of the capacitor in regards to soldering temperature in advance.
When the capacitors are soldered under long duration or high temperature, the dissolution of electrode (leaching), deterioration of adhesion (shear strength) and capacitance decrease may occur.
Take into consideration tombstone phenomenon (also called "Manhattan phenomenon")
for 3216M size or smaller capacitors when the soldering is not proper.
. The tombstone phenomenon can be avoided by taking the following measures:
- reducing land dimensions
- applying adequate preheating
- optimizing solder amount
- ensuring accurate placement
- providing equal heating to both terminations during soldering
- Recommendations to prevent the tombstone phenomenon
- 1) Displacement of capacitor in mounting
Give consideration to minimizing a displacement of capacitor on land of printed wiring board as much as possible. The tombstone phenomenon occurs more frequently when the direction of displacement is same as the reflow soldering direction (movement direction of printed wiring board).
- 2) Mounting direction of capacitor
In designing printed wiring board, give consideration so that the mounting direction of capacitor (lengthwise direction) becomes a right angle to the reflow soldering direction as much as possible.
- 3) Placement of a capacitor among components with larger heat capacity
- ① Reflow soldering direction and printed wiring board direction
Component with large heat capacity
When a capacitor and a component with larger heat capacity are mounted on same printed wiring board, adjust the printed wiring board direction so that the component flows first through the reflow oven for prevention of the tombstone phenomenon.
- ② Distance between a capacitor and a component with larger heat capacity
To reduce the risk of tombstoning, design land patterns placing large heat capacity components in such a way that does not subject capacitors to different temperatures. Confirm by checking the surface temperature of the board.
- ③ Placement of a capacitor with a component of larger heat capacity
The tombstone phenomenon can be suppressed by placing the capacitors in proximity with the side of components with large heat capacity.
At this time, too, place the capacitors as close as possible to the components with large heat capacity and make sure that the capacitor is vertical against reflow soldering direction.
- (4) Pad dimension
Design the pad dimensions so that the land area is as small as possible in order to uniform the solder amount on each land
Mount the capacitor as soon as possible after applying solder paste.
If the interval between applying solder paste and mounting a capacitor is too long, solderability may decrease due to drying and hardening of the solder paste.
Use a suitable amount of solder to form a proper fillet shape.
Excess solder generates high contraction stress and thermal stress. As a result, cracking or breaking of the capacitor may occur. Insufficient solder results in deficient capacitor adherence to the printed wiring board, which may cause capacitor dropout or poor electrical connection which, in turn, may cause reliability to deteriorate. Typical shapes of solder fillet are shown as follows
Note (1) Recommended fillet height: 1/3～2/3 of the thickness of capacitor or 0.5 mm, whichever is
For the fillet height of very small size capacitors, please consult us.
Select an appropriate solder material referring the following notices.
Inappropriate materials can cause troubles such as solder balls.
- ・When solder balls are created, remove any solder balls completely. Solder balls may cause deterioration of electrical property and/or reliability.
- ・Sn-Zn solder may deteriorate the insulation resistance of capacitor under some operating environments.
Safety Application Guide for Multilayer Ceramic Chip Capacitors All Lists