CHAPTER 4 NOTES ON MOUNTING
4.3 BGA Bonding Process
4.3.2 Case 2. Unmelted solder pt.2
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Examples of the measures for each factor of unmelted solder are shown below.
| Measure examples for Factor 1. [Temperature profile] |
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Review the temperature profile:
Check that the recommended conditions have been observed for the solder paste used at the solder joint of the defective device. |
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Change the solder paste:
Use a solder paste that matches the temperature profile used. |
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| Measure examples for Factor 2. [Solder ball oxidation] |
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Review the device storage conditions:
Check that the device's storage environment and conditions (dry pack management, etc.) are appropriate. |
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Review the temperature profile:
Check that preheating temperature is not too high and the preheating time is not too long. |
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Change the ambient reflow atmosphere:
Try executing reflow processing in a nitrogen atmosphere. |
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| Measure examples for Factor 3. [Solder paste deterioration] |
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Review the paste storage conditions:
Check that the paste's storage environment is appropriate and that the storage date has not expired. (Particular care is required when using leftover paste that has been re-stored.) |
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Change the solder paste:
Use a solder paste that matches the storage conditions and management methods used. |
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| Measure examples for Factor 4. [Warping of mounted device/printed circuit board] |
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Review the device and printed circuit board storage conditions:
Check that the storage environment and conditions of the device and printed circuit board are appropriate. |
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Check the printed circuit board and layout of mounted parts:
Check that there is no warping and that parts with a large thermal capacity are not mounted close together. (If parts with a large thermal capacity are mounted close together, it may cause a temperature differential within the device. For details of this phenomenon, see 4.1 Temperature Distribution due to Mixed Mounting.) |
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Check the solder paste print:
Check that the print thickness is adequate and that there are no missing-print defects. (If the amount of print is reduced, the defect may become apparent even if the effect of warping is the same.) |
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Review the temperature profile:
Adjust the temperature profile so that heat is applied evenly to the mounted parts and printed circuit board. |
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