Divergence in Test Results Using IPC Standard SIR and ... · R. esistivity . O. f . S. olvent . E....
15
Divergence in Test Results Using IPC Standard SIR and Ionic Contamination Measurements
Transcript of Divergence in Test Results Using IPC Standard SIR and ... · R. esistivity . O. f . S. olvent . E....
Divergence in Test Results Using IPC Standard
SIR and Ionic Contamination Measurements
Introduction
Ionic contamination testing of PWB’s began in the early 1970’sHobson and DeNoon
PWB assemblies used RMA fluxes and wave soldering. No SMT (Pre Solder Paste) Cleaned with fluorocarbon solvents.
Adopted into military specifications Mil Spec P-28809 and Mil STD-2000A
Evolved into the 1.56 eq µg NaCl limit for cleaned electronic assemblies
+-
+- + - -
Resistivity Of Solvent Extract Test
Test Vehicle rinsed with isopropanol/deionized water mixture.
The ionic conductivity measured and compared to NaCl solution.
Newer methods are automated: Bathtub – Keep same
extraction solution, just circulated.
Shower – Solution passed through ion exchange filter
Usually extract more ionic contamination
+- +
+ --
+-
Some automotive and consumer electronic OEM’s still use the 1.56µg/cm2 NaCl equivalent for qualifying assemblies built with no-cleanmaterials. This limit is given only for cleaned assemblies in J-
STD-001F. Standard to be Eliminated in revision G.Originally intended for Plated Through Hole (PTH)
assemblies using foam fluxers & RMA fluxes cleaned with fluorinated hydrocarbons.
Ionic contamination levels may not necessarily predict electrochemical reliability.
+ -+
- + -+ -
+- -
IPC 9202 provides a better way to evaluate PWB reliability for a given process.As close to actual assembly as possible, using
assembly materials and processSIR measurements using a variety of component
types. ROSE testing can be then referenced to SIR
results. Ionic measurements can then be used as a
benchmark for “future trouble shooting or process control.
+ -+
- + -
Experimental Procedure Preparation IPC B-52 Coupon
Printed & Populated populated
Two solder pastes, A & B SAC305
Reflow straight ramp in N2 1.1 C/s 243°C peak 53 s TAL
Boards cut into 2 parts for SIR & ROSE testing
SIR per IPC TM 650 method 2.6.3.7, 40°C 90% RH 12V bias and measure for 7 days.
ROSE Test Using Ionograph.
IPC-B-52 Test Vehicle
Populated 2,3,5,7,8,10 4 Passives, 1 BGA, 1 QFNPattern 6 Unpopulated
Pattern 6 & 7 Used for SIR
Ionograph 500M SMD II
SampleExtractionSolution(75% IPA25% water)
Extraction tank
Heater
Ion
exch
ange
col
umns
Pump
Conductivity Bridge
Computer
Software
time
CalibrationIntegration
Con
tam
inat
ion
ThermocoupleFlowmeter
Shower-type automated ROSE test
Log SIR Paste A at small QFP leads
High SIR
5
6
7
8
9
10
11
12
13
0 1 2 3 4 5 6 7
Time days
log
SIR
(ohm
s)
Log SIR Paste B at small QFP leads
Low SIR
5
6
7
8
9
10
11
12
13
0 1 2 3 4 5 6 7
Time days
log
SIR
(ohm
s)
Mean IPC-B-52 SIR all patterns testedpastes A and B
5
6
7
8
9
10
11
12
13
0 1 2 3 4 5 6 7 Time days
Log SIR (ohms)
Paste B 0805 Paste B large QFP
leads
Paste B large QFP comb
Paste B small QFP leads
Paste B 0603
Paste A 0603 Paste B small QFP comb
Paste A 0805, large and small QFP bunched together
Paste A is 3 orders of magnitude higher than paste B
Ionic Contamination Measurements Pastes A and B
Paste A has 4X the extractable contamination that paste B has!
Paste A has much higher SIR.
Which method better predicts PWB reliability?
Paste BPaste A
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Equi
vale
nt u
g/cm
2 N
aCl
1.56
Ionic Contamination Measured
Paste A and B SIR per J-STD-004B / IPC-TM-650 Method 2.6.3.7
IPC-B-24 coupons, bare copper on FR-4.
Cleaned in 75%IPA/25% water before printing and reflowing paste.
Paste A SIR is nearly 5 orders of magnitude higher than paste B.
6
7
8
9
10
11
12
0 1 2 3 4 5 6 7
Time (days )
log
SIR
40°C 90%RH 12 V bias and measure 1A
1B1C1D
2A2B2C2D3A3B3C3D
Paste A
Paste B
Conclusions A paste with high SIR can have much more
extractable ionic contamination than a paste with much lower SIR.
ROSE measurements should be benchmarked with SIR evaluation of an PWB assembly process. These measurements should be considered
relative to the SIR evaluation. ANSI/IPC J-STD-001F will be amended to
account for the divergence in SIR and Ionic contamination results on electrical reliability
+ -+
- + -
-+
Mitch HoltzerAlpha Assembly Solutions109 Corporate Blvd.South Plainfield, NJ 07080
