Pilots have been required to carry plastic certificates since 2010, but the deadline for replacing other paper FAA certificates, such as mechanic, repairman, flight engineer, or ground instructor, is coming up March 31. You still have time to meet the deadline, as long as you apply online, which takes about 7 to 10 days for processing. Mail requests will take 4 to 6 weeks to fulfill. Each certificate replacement costs just $2. If you'd like to keep your old paper certificate, you can, but it will no longer have any official authority.
Temporary certificates and student certificates are exempted from the rule, and will remain valid until the expiration date. The FAA launched its effort to replace paper certificates back in 2005, mainly in response to security concerns. The new plastic cards are more difficult to counterfeit.