How Cleaning PCBs Helps You Achieve Zero Defects

Dec 14, 2020
| By Tracy Riggan

Key Summary

• A small reduction in peak reflow temperature can increase contamination on printed circuit boards by up to 600 percent.
• Cleaning becomes more essential as board density, voltage levels, and residue levels increase, especially for automotive and other high-reliability applications.
• “No-clean” flux does not mean “do not clean,” since residues can still cause electro-chemical migration, corrosion, or frequency distortion.
• Foreign object debris has caused real-world failures and recalls at major automakers, highlighting the financial value of proper cleaning.
• Coating no-clean boards can trap residues and allow moisture intrusion, reducing long-term reliability if cleaning is skipped.

How important is it to clean printed circuit boards to avoid electrical defects? According to Mike Konrad, Aqueous, a 4 percent reduction in peak reflow temperature can increase board contamination by up to 600 percent. This factor was one of many I took from Mike’s recent webinar, “The Proliferation of Electronics into Harsh Environments and the Effects on Reliability,” held on December 3.  For applications where performance is critical and any failure catastrophic, cleaning takes risks like process temperatures or board handling out of the equation and can do so for very little cost (Aqueous’ Tips & Tricks: https://vimeo.com/440157202/a864b0237a).

Another valuable point Mike made is that using “no-clean” flux doesn’t mean “don’t clean” – it just means, “clean if you need to.” As board density increases, making boards less tolerant of any type of residue, boards operate at higher voltages, and increased residues are present on the board (human and manufacturing process related), automakers will likely be choosing to clean more assemblies to prevent ECM, corrosion, or frequency distortion for long-term reliability. Mike provided examples from BMW, Ford, and Hyundai where foreign object debris caused recalls for issues such as sudden power loss, shutdown and battery fires, indicating to me that the financial investment in cleaning is worth it.

And, while there are solutions to reduce debris and conductive residue, Mike explained that coating no-clean boards locks in any process residues and won’t prevent moisture from leaking in, causing electro-chemical migration and parasitic electrical leakage issues, impacting board reliability. Mike mentioned many documents which address aspects of this, which I’ve linked to below for your reference. If you have board reliability challenges or solutions that need to be addressed, we invite you to join the automotive electronics standards development effort. We welcome increased collaboration and problem-solving to serve automotive reliability needs.

To view Mike’s webinar on demand, register at: https://tinyurl.com/IPC-Konrad

Resources mentioned in webinar:

Q:
Why does cleaning printed circuit boards matter for reliability?
A:

Cleaning removes contamination and residues that can lead to electro-chemical migration, corrosion, short circuits, and long-term electrical defects.
 

Q:
Does using a no-clean flux mean I should avoid cleaning?
A:

No. No-clean flux means cleaning is optional, not prohibited. If residues or reliability risks exist, cleaning is still recommended.
 

Q:
How does reflow temperature affect board contamination?
A:

According to Mike Konrad, a 4 percent reduction in peak reflow temperature can increase contamination levels by up to 600 percent.
 

Q:
Why are automotive manufacturers cleaning more assemblies?
A:

Automotive electronics face harsh environments and operate at high voltages. Increased residue, board density, and safety requirements push automakers to clean more assemblies to avoid recalls and failures.
 

Q:
Can conformal coating replace the need for cleaning?
A:

No. Coating can trap residues and still allow moisture intrusion, which can lead to electro-chemical migration and parasitic electrical leakage. Cleaning remains essential before coating.