David Bao

David Bao has submitted responses to the following questions.

Solder Paste Prep Before Use
1.5 - 2 hours may not be enough to let the solder paste equalize with ambient temperature. My recommendation is ...

LED Component Shift During Reflow
There many root causes for components drift during SMT reflow process:Ramp up rate too high at reflow stage. High ramp ...

Can a Few Contaminated Joints Cause an Assembly to Fail RoHS Compliance?
Yes, a few contaminated solder joints will cause you fail RoHS compliance. Lead contend for every solder joint on the ...

Exposed Copper Risk
Yes, you do have a potential corrosion issue. You may use conformal coating to spray on the exposed copper on ...

Tiny Solder Balls After Reflow
Random solder balls can be caused by different factors. If solder balls appear only on the printed area, the root ...

Selective Soldering Frame Causing Cold Solder Joints
The selective soldering frame is one of possible root causes for cold solder joints. Other root causes might be insufficient ...

Soldering Components with Silver Pads
Using Ag containing alloy, such as Sn62Pb36Ag2, will reduce the Ag leeching issue. You may also try a different solder ...

Solder Paste Mixing
We do not recommend using a centrifuge machine to mix solder paste. Unopened refrigerated paste should be allowed to reach ...

Solder Paste Viscosity
A simple method to distinguish Leaded and Lead-free solder paste will be a simplified solder ball test (IPC-TM-650). Use stainless ...

Solder Paste Viscosity
The factors that affect solder paste viscosity are paste flux, metal load and powder size. Finer powder size will increase ...

Lead Free Reflow Oven Zone Count
For lead-free soldering, I will recommend at least a 7-zone reflow oven, which will give you flexibility to properly design ...

Concerns With Silver Finish Component Leads
Small amount of silver from component will not cause reliability issue metallographically in solder joint. However, silver leaching may weaken ...

Frequency of Checking Solder Paste Viscosity
The solder paste users do not need to check the viscosity once it is qualified for their process. It is ...

Contamination Using Solvent Dispensers
Yes, your solvent is contaminated every time when you put the brush back to the bottle, which will cause additional ...

HASL vs. Immersion Gold
Generally speaking, hot air solder leveling (HASL) as a finish on circuit boards provides better corrosion resistivity than immersion gold. ...

Wave Solder Pot Contaminated with Lead
Decant about 40-50% of the pot and replace it with the same lead free solder bars. The solder decanted out ...

Wave Solder Pot Alloy Adjustment Formula
Theformula for adding pure tin to restore the alloy to 63/37 is: W(Sn)= (0.63-0.624)*W(ap)/0.37 W(Sn):Weight of tin need to be ...

BGA Joint Voids - Accept or Reject?
This BGA definitely has too much voiding and needs to be corrected. Whenever this much voiding forms in a single ...

Reliability of Automated Soldering vs. Hand Soldering
It is a well-known fact that hand soldering is a much less controlled process than the SMT process. If it ...

Reduced pH and Specific Gravity of Flux
If the same flux is used, when both pH value and the specific gravity are reduced, it usually means the ...

Solder Paste Life on the Stencil
Since the original solder paste has been mostly replaced with the fresh paste, you do not have to change the ...