Testing of Solder Joints to Printed Electronic Traces on Flexible Polymer Substrates. Jeffrey Parker Printed Electronic Product Specialist Insulectro

Transcription

1 Testing of Solder Joints to Printed Electronic Traces on Flexible Polymer Substrates Jeffrey Parker Printed Electronic Product Specialist Insulectro

2 Soldering to Printed Silver Filled Traces Soldering to printed silver on PET/other films, was difficult Temperature concerns with substrates and printed traces Silver leaching from trace Adhesion issues after soldering Testing protocols do not exist Proper type of solder/flux to use Equipment considerations/process

3 Soldering to Printed Silver Filled Traces

4 Why Solder to Printed Traces? Solder forms an alloy as opposed to a conductive adhesive bond to a printed trace No compatibility issue between adhesive and printed trace Provides a superior electrical connection to a silver trace With an encapsulant, the bond is extremely robust Solder joints can be formed rapidly minimizing heat to the entire part Large ovens or dryers are not needed for processing Silver ink with SAC 305 solder

5 Drawbacks of Soldering to Printed Traces Equipment needed may be unique to current processes Testing protocols have not been developed Fixtures for testing will need to be modified from existing equipment Need to ensure the correct product set Rework is not easy and many time not possible Need to get it right the first time

6 Structural Support Silver Trace (0.4 mil thick) Solder Joint to Silver Trace PET Substrate (5 mil thick) As a standalone feature, solder joints to silver traces, printed on PET have little strength There is no adhesive strength between the solder and the PET Adhesion relies solely upon the attractive forces between the silver trace and the PET

7 Solution -- Encapsulation Non-Conductive Encapsulant Silver Trace-0.4 mil Solder Joint to Silver Trace PET Substrate (5 mil thick) Based on experience with encapsulating components using conductive adhesive Would recommend that the encapsulant cover as much area on bare PET as the trace/solder area This will provide good constructive strength for the soldered area

8 Importance of Encapsulation Left unencapsulated the solder joint has limited adhesive strength and may not adhere Other forms of encapsulation could be used such lamination with sheet adhesives Encapsulation should be selected for strength adhesion and compatibility

9 Causes for Solder Joint Failure Traditional solder joints have a fillet cross-section The failure shown here is catastrophic, causes; - mechanical stress - vibration - thermal shock Other issues stem from a variety of problems that can be process related or due to improper compatibility From the VFA Engineering Group From Adafruit Learning System

10 Causes for Solder Joint Failure on Film This particular failure was caused from stress due to flexing The failure was caused by delamination of the ink to the PET substrate Need to select the proper ink/substrate combination to ensure the best possible adhesion before applying solder The most commonly accepted test for optimal adhesion is the tape test, along with conductivity

11 Testing for Solder Joints on PET A sheer force test can be used which is an industry standard for die attach material and solder adhesion.

12 Mandrel Bend Testing This process can test to failure or to a loss in conductivity when observable failure is not obvious Gardco

13 Other Forms of Testing Other forms of testing are: Vibration Thermal Shock Environmental testing US Koshin ESPEC North America

14 Summary Soldering to printed silver traces is a viable option Ensure the proper solder/flux combination is used Encapsulation is recommended for robust performance Testing methods can be derived from existing protocols Need for performance targets to be established

15 Thank You Jeffrey Parker Printed Electronic Product Specialist Insulectro (603)