The power of using a Wetting Balance for solderability testing over Dip and Look Testing

The power of using a Wetting Balance for solderability testing over Dip and Look Testing

                                                                CASE Study # 1

 

Background: a client is looking to evaluate the impact on the solderability of an ENIG deposit as the Immersion Gold Bath ages through its normal metal turn overs (MTO’s).  Depending on the supplier of the Immersion Gold chemistry, a typical bath “life” runs between 4 to 6 MTO’s. A metal turnover is defined as when the original metal content of a freshly made up plating bath is replenished. Example if a new Immersion gold bath contained 50 troy oz.’s of gold, then when 50 troy oz.’s was replenished to maintain the bath concentration within specification then it would be described as being at 1MTO.

The ENIG specification IPC 4552A contains pass/fail criteria for wetting balance testing as well as the IPC JSTD003C WAM2. This makes testing the standardized wetting balance coupon very simple and provides instantaneous accept or reject criteria without the need to visually inspect and measure wetting coverage as required by dip and look type testing.

 

Parameter

Description

ENEPIG

I Sn

ENIG

To ‘‘as received’’

Time to buoyancy corrected zero

≤ 1.5 seconds

≤2 second

≤ 1.5 seconds

To ‘‘post stressing’’

Time to buoyancy corrected zero

≤ 2.5 seconds

≤3 second

≤ 2.5 seconds

F2

Wetting force at two

seconds from start of test

≥25% of maximum theoretical

wetting force at or before

two seconds

25% of maximum theoretical

wetting force at or before

two seconds

≥25% of maximum theoretical

wetting force at or before

two seconds

F5

Wetting force at five

seconds from start of test

At or above the value of F2

At or above the value of F2

At or above the value of F2

Minimum force

‘‘as received’’

At ten seconds

>0.19mN/mm

0.15mN/mm

>0.22mN/mm

Minimum force

‘‘post stressing’’

At ten seconds

>0.17mN/mm

0.12mN/mm

>0.19mN/mm

Figure 1: the current list of PASS/FAIL criteria for PWB surface finishes – this is for Pb-free solderability testing, a different set of requirements exists for testing with SnPb solder

 

Figure 2: typical wetting balance test array used for this testing

 

Figure 3: Merge of 5 Wetting Balance Test Immersion gold bath  – meets IPC JSTD003C WAM 2 requirements

 

Figure 4: Average of 5 Wetting Balance Test Immersion gold bath  – meets IPC JSTD003C WAM 2 requirements

 

Figure 5: Merge of 5 Wetting Balance Test Immersion gold bath at 0.5 MTO – meets IPC JSTD003C WAM 2 requirements.

Figure 6: Average of 5 Wetting Balance Test Immersion gold bath at 0.5 MTO – meets IPC JSTD003C WAM 2 requirements.

 

 

Figure 7:  Merge of 5 Wetting Balance Test Immersion gold bath at 1.0 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 8:  Average of 5 Wetting Balance Test Immersion gold bath at 1.0 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 9:   Merge of 5 Wetting Balance Test Immersion gold bath at 1.5 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 10:  Average of 5 Wetting Balance Test Immersion gold bath at 1.5 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 11:    Merge of 5 Wetting Balance Test Immersion gold bath at 2.0 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 12:  Average of 5 Wetting Balance Test Immersion gold bath at 2.0 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 13 :  Merge of 5 Wetting Balance Test Immersion gold bath at 2.55 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 14:  Average  of 5 Wetting Balance Test Immersion gold bath at 2.55 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 15 :  Merge of 5 Wetting Balance Test Immersion gold bath at 3.05 MTO – meets IPC JSTD003C WAM 2 requirements.

 

Figure 16:  Average  of 5 Wetting Balance Test Immersion gold bath at 3.05 MTO – meets IPC JSTD003C WAM 2 requirements.

 

 

Figure 17 :  Merge of 5 Wetting Balance Test Immersion gold bath at 3.55 MTO – meets IPC JSTD003C WAM 2 requirements.

 

 

Figure 18:  Average  of 5 Wetting Balance Test Immersion gold bath at 3.55 MTO – meets IPC JSTD003C WAM 2 requirements.