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Bryan Kerr
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Principal Engineer - CMA Lab
BAE Systems
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.

Bryan Kerr has submitted responses to the following questions.
Long Term Component Storage
Preservation of solderability for such a long period of time would involve mitigating the two main reasons for deterioration of ...
Solder Balls During Rework
If you melt solder underneath conformal coating it will expand in volume and normally burst out of the coating and ...
Dendritic Growth and Contamination at BGA Sites
Electrolytic corrosion resulting in dendritic growth results in metal crystals across the isolation zones and, although difficult to clean thoroughly, can ...
What is Causing Oxidation?
Black tarnishing on silver is most likely caused by some form of sulphur contamination creating silver sulphide often seen as ...
Spec for Baking Assemblies Prior to Rework
There are a number of factors which determine the susceptibility of any particular PEC assembly to moisture absorption and the ...
Delay Before Washing Water Soluble Flux
The residues from most water soluble fluxes should be removed as promptly as possible since they may begin to cause ...
Ideal Relative Humidity for Final Assembly
There are two scenarios to consider here. Low humidity will make the risk of ESD damage greater and you should ...
J Lead Overhang Specification
According to J-STD-001D Table 7.7. the toe overhang must not violate minimum electrical clearance. In this case I would estimate ...
Best Way to Eliminate Dross?
Dross is produced by movement of molten solder in air producing tin and lead oxides. Reduction in exposure to air ...
Soldering Quality & IPC Standard?
A prerequisite of any solder joint is that it must be homogenous and, regardless of the IPC standard, this type ...
Conformal Coating Cross Contamination
Silicone is certainly the material most likely to cause problems if contaminating other product since it can cause problems with ...
Bottom Side Component Attachments
This question needs further clarification and possibly a few photos. ...
Bottom Side Component Attachments
This does kind of depend on the reason for the solder attach as suggested by your sub-contractor. For heatsinking you ...
Wave Solder Pallets
I would recommend that you use separate pallets and identify them as such. Tin/lead solder particles and dross can be ...
Component Storage Recommendations
There are several mechanisms which will degrade solderability dependant on the type of finish. Oxidation or corrosion which are influenced ...
No Clean or Water Soluble for QFN Components
These component types have very low stand off heights and will be very difficult to clean underneath. Water soluble flux ...
Solder Fillet Peaks
There are a few things you could try to eliminate the peak. Vary the direction of wipe off to encourage ...
Recommendation for PCB Surface Finish
There are a few options all with their related good and potentially bad points. Immersion tin is a thin tin ...
Cleaning No-Clean Solder Paste
Your problem is a combination of how good your solvent is at removing this particular flux and the fact that ...
Soldering lead-free component, with tin-lead solder
Mixing of lead free solder and tin/lead solder balls will result in an alloy somewhere in between and you should ...
Problems with Bubbles in Conformal Coating
Bubbling normally occurs because the solvent in the coating does not get a chance to evaporate off before the surface ...
Problems with Insufficient Barrel Fill
As with tin/lead wave soldering lack of barrel fill is almost always heat related although poorhole solderability is a possibility. ...
Re-plating lead-free components for tin/lead assembly
If you want to eliminate any risk of tin whiskers occurring you really need to replace the tin finish with ...
Long Term Concerns with Disturbed Solder Joints
Definition of a disturbed joint is one which has moved during solidification. This produces a distorted structure with lines of ...
Cause of Unusual Contamination?
This contamination appears to be due to particles of solder paste being present across the surface during reflow. These have ...
What Is the Life Span for a Profile Board?
The lifetime of a test board is dependent on the type of substrate and the PEC construction. As long as ...
Concerns Using Aluminum Flux Tank
Aluminium is chemically attacked by acid solutions and, as such, the water soluble flux is not compatible with this material. ...
How To Prevent PCB's Warpage When Baking
If your PEC's are warping during bake then they are likely to warp during reflow so constraining them is probably ...
Tombstoning Dilemma
Tombstoning can have a variety of causes but check for the following. Are the PEC pads on both sides identical ...
SMT Component Lead Oxidation
This kind of depends on the termination style - leaded components can be pre-tinned using more active flux if necessary ...