Lead-free: Polymers at high temp
‰ Lead free processing temperatures will be significantly higher than tin-lead processing temperatures
‰ Customers are providing input that may require thermal stability through 260 C
‰ This may have a negative impact on the cost of the connector solutions
‰ Current materials, such as PBT, may not perform well in lead free reflow environments.
The approach is to
• Determine the thermal properties most important to polymer selection for lead free processing
• Test polymers in wave and reflow environments
– Wave solder resistance to soldering heat test method
– Reflow solder resistance to soldering heat test method
•If both the HDT and the melt temperature are above the solder process temperature then the plastic will likely perform well.
•If both the HDT and the melt temperature are below the solder process temperature then the plastic will likely fail during soldering.
•If the solder temperature is in between these two values then the product must be evaluated for performance.
‰ Solder melting temperatures
• Sn/Pb = 183 C
• Sn/Ag/Cu = 217 C
• Sn/Cu = 227 C
‰ Reflow solder
• Sn/Ag/Cu reflowed at temps as high as 260 C
• These product processed according to reflow profile on the next page. Max temp = 260 C
• PCI card edge connector
• Critical dimension is the slot for the daughter card
• Top – high temp nylon showing no distortion
• Middle – PCT showing minor distortion
• Bottom – PBT showing major distortionTechnology
Polymers: What is a failure?
- ‰‰ Once joined together, the board lock has not further function.
- Thus, its condition is not relevant.
- ‰ Thus, if the polymer has low or moderate thermal stability, the product engineer will need to determine if melting or distortion would lead to failure – in that particular product.
- ‰ The heat from wave soldering can transmit up the contact to the contact polymer interface.
- Excessive heat at this location can lead to distortion or a reduction in contact retention strength.
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