IPC-7530A Draft Document for Industry Consensus Only August 2016
The time difference between inner and outer balls becoming liquidus is called Liquidus Time Delay (LTD), and plays a critical role in HoP. Hence True TAL must be sufficient for ALL balls (60 seconds). Also to minimize HoP, avoid too long soak and ensure min 235 o
C Peak for all balls. When dealing with backward compatibility situations,
(lead free BGAs being soldered with predominantly tin lead components and solder paste because tin lead BGAs may not be available) strive for 232 o
C minimum peak. To minimize HoP, use ramp to peak profile instead of ramp to soak profile but do understand that ramp to peak profile may result in more voids in BGAs. It is a balancing act but voids are not serious defects, but HoPs are. Here are some specific Reflow Guidelines for Lead Free, Peak and
TAL
1. Peak Target 235 to 245 C but aim for 240+/- 2C
2. TAL Target above 220C: 60 to 90 Seconds. Shoot for 70 Seconds
3. True TAL Target: 60 Seconds for All BGA Balls
4. TAL Target above 235: 20-30 Seconds. Shoot for 20 Seconds
5. TAL Target above 240 C: 5 to 15 Seconds. Shoot for 10 Seconds
Fine point note: It is understood that over the area of large components not all locations of that component will reach liquidus at the same time; some later than others.
3.4 Equipment Settings
3.4.1 Reflow Oven Selection
Reflow ovens are available in various sizes and configurations. When selecting the most appropriate reflow oven for a particular purpose, many variables should be taken into account in terms of types of devices being assembled and types of configurations/options. Such options that should be reviewed in terms of a product application include:
• Size of product
• Desired throughput
• Types of solders
• Types of fluxes
• Cost of assembly
Such options to be considered regarding ovens include:
• IR or convection number of heating zones
• Clearance height
• Cover gas
• Conveyor belt type
• Belt width
• On-board profiling ability
•
Product tracking
22