Low Ag Alloy Solder Paste Reliability

 

Phase 1 process feasibility study of low Ag alloy solder paste showed that the candidate materials tested can be used in the process without major assembly defects. Phase 2 will evaluate the reliability of these solderpaste. Phase 2 Reliability is a 2 leg project. The first leg will assemble and test a QFN component to down select alloys for next BGA leg. Leg 2 will assemble and test a BGA component with a SAC305 solder ball and the various candidate solderpaste.

 

 

Project stage: 
Lead company: 
Nokia

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Idea Information

Background: 

Low silver alloy (such as SAC105) for the BGA solder balls are being used in product.  Within the past couple years, many alternative low/no silver alloy solder pastes have been developed and are available in the market.

Phase 1 process feasibility study of low Ag alloy solder paste showed that the materials tested can be used in the process without major assembly defects.

Low Ag/High Temperature solder pastes (mp >217degC) can be assembled using the typical lead-free process window. However, longer reflow time may be needed depending on the peak temperature.

Low Ag/Low Temperature solder paste (with lower Bi%) (mp<217degC) can be assembled at reflow temperature of <230degC.

This Reliability Phase 2 which will study the reliability of a set of the candidate low/no Ag alloy solderpaste from Phase 1.

Phase #1: Low Ag /High Temperature Solderpaste Candidates

 

 

Phase #1: Low Ag /Low Temperature Solderpaste Candidates

Problem: 

The price of metals and particularly silver (Ag) has been increasing in recent years. This has created an increased interest in the use of low/no silver alloy in the manufacturing process. Low silver alloy BGA solder balls (such as SAC105) are being used in products, but there is very little information about the alternative (low/no) silver alloy solder pastes, it’s process feasibility and reliability. Phase 1 process feasibility study of Low Ag alloy solder paste showed that the materials tested can be used in the process without major assembly defects.There is very little information about the alternative (low/no) alloy solder paste, its process feasibility and reliability. (Reliability studies have been done for the alternative low/no silver alloys solder balls). There is a need to reduce the assembly cost for some products. There is also a need to expand the process window by lowering the process temperature. As there are no industry projects that we are aware of on low/no silver alloy solder paste, this project will evaluate the reliability of a selection of candidate solderpaste.

Definition Information

Goals / Benefits: 

Goal:

  • This project will study the reliability of low/no silver alloy solder pastes including

–      Low/no silver high temperature alloy solder pastes (liquidus temperature >217°C)

–      Low/no silver low temperature alloy solder pastes. (liquidus temperature <217°C)

  • Phase 2 Reliability is a 2 leg project.

–      Leg 1: QFN component to down select alloys for next BGA leg

–      Leg 2: BGA component testing to be presented to the BOD once QFN testing is completed.

 

Benefits:

  • Low Ag / High Temperature Alloys can enable a more cost effective product though the reduction of silver usage. (This will benefit both CMS/EMS and OEM/ODM’s)
  • Low Ag / Low Temperature Alloys can extend the temperature headroom for assembly. We are running out of temperature headroom with Pb Free especially for large components. (This will benefit the CMS/EMS and component suppliers)
  • Low Ag / Low Temperature Alloys can provide a more flexible product, example; Hand Soldering can be done at lower temperatures and lower rework damage. (This will benefit CMS/EMS)
  • Low Ag / Low Temperature Alloys can improve reliability of the final product by lowering thermal stress and warpage on the components/PBCA. (This will benefit OEM and OEM Customers)
  • Low Ag / Low Temperature Alloys are more Environmentally Friendly. They lower ground pollution, lower energy consumption by lower processing temperature. (This will benefit the Global Population and reduce the carbon footprint of products for the OEM).
  • The wider acceptance of Low Ag Alloy will open markets for our Alloy Material Suppliers. (This will benefit the Alloy Suppliers)

 

High level objectives: 

 

Objective:

The QFN leg will provide data on reliability of Low Ag Alloy Solderpaste and compare the data with SAC305.

  • The team will build and assemble a set of QFN TV’s to test both high and low temp - low Ag Alloy Solderpaste.
  • These TV’s will be thermal stressed at -40 to 125 C to test the solder joint reliability and compare to a SAC305 baseline.
  • The team will then downselect the solderpaste for the BGA leg.

Metalurgical Analysis will be completed on the solderpaste after thermal cycling like the following picture of a SAC 305 ball with SAC 305 paste

Deliverables:

Provide the HDP membership the reliability data of Low Ag Alloys solder pastes tested

The team will publish a coded version of the results in a paper/presentation at a major conference (SMTA/IPC) to help encourage the industry to accept alternative alloys solderpaste

Approach: 

This project will assemble a set of TV’s with QFN components using the candidate low/no Ag solderpaste from Phase 1 and thermal cycle these TV’s from -40 to 125 C until we have at least N50 data on their reliability.  A BGA leg has been proposed as a follow on project to test the reliability of the BGA component and the mixed alloys.

 

 

Key Participants: 
Celestica
Cisco
Engent
Flex
IBM
Indium
Juniper
Keysight Technologies
Nihon Superior
Nokia
RBP Chemical Technology
Sanmina
Senju Comtek
TTM Technologies
WUS
Public