Thermal and Process Sensitivity Beyond ICs

Estimated reading time: 4 minutes

BY Jack Crawford, IPCSemiconductor components that go through reflow can be damaged by heat. That has been known for a long time. IPC-J-STD-20, “Moisture/Reflow Sensitivity Classification for Non-hermetic Solid State Devices,” is in place for moisture sensitive devices (MSDs). However, lead-free processes brought about the need for another look at the effects of temperature, as board failures due to component damage that occurred during processing started to rise dramatically.

In the switch to lead-free solder, board assemblers had to raise their reflow temperatures by 5° to 20°C, from 320°C to as much as 340°C. Under these conditions, passive components melted, warped, cracked, delaminated, or even exploded. Further, there wasn’t any standard to cover components used in wave solder processes. Cleaning processes were another potential source of damage. A new standard was needed to cover thermal issues and process sensitivity that affected components other than semiconductor devices. The result, ECA/IPC/JEDEC J-STD-075, “Classification of Non-IC Electronic Components for Assembly Processes,” was released in September 2008.

ECA/IPC/JEDEC J-STD-075 Standard

J-STD-075 picks up where J-STD-020 left off. The purpose of this specification is to establish an agreed set of worst-case solder process limits for both tin/lead (SnPb) and lead-free alloys and thermal limitations for safely assembling components on common substrates such as FR-4, ceramic, and polyimide, along with documenting commodity-specific exceptions. For all semiconductors, it also covers issues that aren’t part of J-STD-020. The standard outlines a process to classify, label, and evaluate components’ process sensitivity level (PSL) and moisture sensitivity level (MSL). Component manufacturers and suppliers, users, and assemblers must be highly familiar with this standard’s information and processes to ensure optimal product quality and reliability.

Three industry associations collaborated on IPC-J-STD-075: IPC – Association Connecting Electronics Industries; the JEDEC Solid State Technology Association, which develops standards for integrated circuits (ICs); and the Electronic Components Association (ECA). The urgency and importance afforded this standard translated into its publication in just eighteen months.

“Even though suppliers had tested their parts and declared them capable of withstanding the higher temperatures of lead-free soldering, some components were encountering problems because of the confluence of several factors on the PCB,” said Paul Krystek, technical program manager at IBM and lead cochairman of the ECA/IPC/JEDEC J-STD-075 committee. “Board thickness, layer count, and component placement all determined the amount of heat that a device would be subjected to and for how long.” The standard defines a process by which suppliers can evaluate their components against these base profiles and classify parts as process sensitive or not.

The component evaluation process begins with the supplier looking at all component families against each base solder process condition defined in J-STD-075 and classifying the PSL. Components that cannot meet base conditions are defined as process sensitive. If the component can meet a defined solder process condition, its MSL shall be evaluated using that solder process condition and J-STD-020.

The same process is used for all SMT components and selective thru-hole components where the supplier has specifically documented support for reflow soldering (paste-in-hole/selective soldering) for a specific component or component family. This includes lead-free soldering. The base reflow solder process conditions are defined by J-STD-020, where the peak temperature (classification temperature – Tc), is specified as a function of the component size. All temperatures are measured on the top center of the component body (package body surface facing up during assembly reflow), except connectors. Due to the range of unique connector designs and significant process sensitivity variability among connector suppliers, the connector supplier’s specification should be used for temperature measurement location definition. A table of exceptions is given in the standard.

The component’s PSL shall be evaluated and classified to the worst-case process limits as outlined in its specification; a classification scheme is part of the standard.

PSL classifications will always have at least two characters and there may be an optional third character. The first character defines the process being limited, with “W” used for wave or “R” for reflow soldering. If a component meets or exceeds the base solder process conditions, PSL values of “W0” and/or “R0” apply. The second character identifies the Tc. A third character is optional and identifies other process limitations. These designations are intended to minimize confusion with J-STD-020 moisture sensitivity levels.

Conclusion

Only components classified as process sensitive must be labeled. According to the standard, component manufacturers shall publish their component’s PSL classification and label (machine printed) first-level containers such as tape and reel, bag, or box with the PSL classification when the second character of the PSL is >0. Specific labels are given for wave solder and reflow. If a component is both wave solder and reflow process sensitive, both classifications shall be labeled.

IPC, JEDEC, and ECA standards and publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining – with minimum delay – the proper product for a particular need. As a result of a team effort, we now have a document that classifies components so assemblers are able to know of problems that may occur with certain components. SMT

Jack Crawford, director of certification and assembly technology, IPC – Association Connecting Electronics Industries®, may be contacted at JackCrawford@ipc.org.