Bubble and overflow glue are common questions of FPC quality.Coverlay flow follow press temperature go up lead to copper pad adhesion glue like epoxy.
The reasons of glue overflow
It involve many aspects,like coverylay protection in process,FPC factory technology parameter,environment protection,worker operation,etc.
One of reasons: Coverlay parameter when making.
When CL is coating and baking,if the temperature,time and parameter controlled improper,it will cause glue overflow in prepreg.
The second reason: Coverylay storage environment
The correct storage environment temperature is under 10℃,optimum storage environment temperature is 0℃－5℃,validity period is 90 days.if the storage temperature is incorrect, coverlay is easily absorb moisture and go into stability lead to glue overflow.
The third reason: If CL match FCCL
In the design of layer stackup, FCCL and CL need coherence. If the thickness of Coverlay and Copper have big different, it’s easier lead to glue overflow.
The fourth reason: The design of FPC
Follow the high density interconnector products approach,appeared isolate pad design lead to glue overflow.
The fifth reason: FPC technology parameter
In set up of FPC technology,like pressure is overstrong,time is overmore, press machine’s press is inequality,all these factors can lead to glue overflow.
The solution of solve glue overflow:
We have know the reasons lead to glue overflow,so we can make different solution for different problem.
Coverlay making problem:
FPC factory should strict inspection the incoming material,if any unqualified material should return to supplier avoid effect FPC fabrication.
Storage environment
As validity period of CL is less than two months,so FPC factory should have freezer to store the CL materials.If CL got moist as save improper,they can through low temperature baking the CL before use and temperature should be 60－80℃；2~4 hours, it will great improve the glue overflow problem.
Isolate pad
This kind of phenomenon is the most common quality problem of all FPC factories. If we change technology parameter as glue overflow problem,it will bring bubble or peel strengthen problems.if miscontrol of glue overflow,need use 2% NaOH to immerse and through brush machine can clean glue smear.
In press process, operator need strict follow instruction to make register, and strengthen inspection control avoid register inaccurate lead to glue overflow.
At the same time, factory need strict follow 5s to inspection if CL be contaminated,if have burr, develop workers with good operating habit,improve productivity.
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