Subject:                               Time:10:02 AM
  OFFICE MEMO          ASSY: Non-wetting                      Date:4/23/97

Hello everybody:

I have the following case study that I would like to share and get your comments before arriving to a conclusion.
Problem: Non-wetting on  90% (RM0705) chip resistors (different values), 100% grainy solder joints on chip components (RM0705), ceramic flat packs show shiny and smooth solder joints on the same assembly.  Non-wetting accentuated after second reflow.
Process: 
-Vapor Phase (216oC) with infrared preheat system, Solder Paste Sn63/Pb37 RMA
-Profile: shows that some Temp across the PWB were between 180oC to 187oC before entering to the vapor (reflow)

Background & Tests: 
- Chip components belong to different lots (different values) but same part type
- Lots are 2 year old!!
-Termination: Metallization: fired platinum-gold, vacuum deposited nickel chrome, electrodeposited nickel, electrolytically deposited gold, and then coated with Sn60/Pb40 (QQ-S-571)
-SEM/EDX results show oxidized termination (lead oxide) and traces of Phosphorus
-Solderability test "Dip & Look" per ANSI/J-STD-002 using:
     R Flux: did not pass
     RMA Flux: pass


Thank you in advance for any inputs,

Gino Cochella
(310) 814-3955
e-mail: [log in to unmask]

            

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