Plastic boss crack of mold-in screw insert potential cause

Recently field complained our product had plastic house broken issue. As checked the defect parts and found the crack came from the screw boss till outside house. There is a mold-in screw INSERT part inside the boss. Below will list the screw boss crack potential causes:

LCM gasket/cushion design

LCM (LCD Module) is a common component for the electronic products. Almost of the LCM was made by glass and it is brittle and  break easily while hit or drop on the floor due to handle careless. As product design we will install a rubber gasket or cushion locate between the glass and plastic case or metal bezel to prevent it from squeezing due to press or careless hitting.

Although this kind of rubber gasket is a simple design but if the gasket didn’t design well then the installation will be a big challenge in manufacturer. We often see the gasket go outside of the display view area. If this is a touch panel product then it will result the touch function fail. If this kind of issue happens in filed then we will get big trouble.

Therefore, this article attempts to look for the rubber gasket design methods.

Humidity temperature cycle

The humidity test is designed to determine the effects of humidity on the product and assure that the product will meet published specifications while being subjected to high humidity conditions. This is an accelerated test to uncover failure modes in components, assemblies and process, which may appear in the field during normal service, while keeping test time at a minimum. Performance tests are made at various intervals of the test duration and each test must pass for the design to meet the requirements of this section.

Hygroscopic materials (e.g., printed circuit boards, molded plastics, sealed components, etc.) will absorb moisture proportional to the applied vapor pressure and time of application. Excessive moisture penetration may cause swelling of material or contamination actions, destroying functional ability as well as causing leakage paths between sensitive circuits, result when moisture reacts with trapped chemicals from construction processes causing corrosion or severe etching of metal surfaces. In some cases dendritic growth can cause short circuits or high voltage flashover between closely spaced traces or pin spacings. The following humidity test is designed to accelerate the occurrence of these failure mechanisms if they exist.

Temperature Environmental test

The purpose of temperature environmental test is that the good are shipped by various types of carriers and experience a wide range of storage temperatures, depending on the customer environment, hence the need for this kind of testing. Further, certain components and assemblies are sensitive to these temperature extremes and could be weakened due to induced stresses. Therefore, it is important that a logical sequence of testing be followed in order to observe these effects and assure the product’s performance under various temperature conditions and after temperature extremes have been applied.

(Note: This test didn’t include the humidity.)

Using Shielding can clip to instead of shielding frame

For almost of the frequency radio apparatus, the Printed Circuit board must design the shielding frame/can to prevent the EMI (Electromagnetic Disturbance Interference) effect. The regular design will apply one shielding frame to mount on PCB by solder and another shielding can to cover on the frame to isolate the RF.

That means there will be two press tools cost before implement this solution. Beside, the shielding frame must be mounted on the PCB by SMT process. It requires lower flatness specification to keep the solder joint well. Most of the shielding frame asks its flatness meet 0.12mm maximum. Some of the shielding frame even asks the flatness must lower than 0.10mm maximum. Because of current stencil thickness is around 0.10~0.127mm only. It brings more difficult to form the shielding frame and raise its cost.

The actuator design for right angle connector

Recently my company met lots of component broken troubles for the electrical connector call “right angle connector” or “flip lock connector” in manufacturing production line. We found almost the defect connector broke at the ACTUATOR portion while operators first time tried to lift it after SMT high temperature reflow process. I’m sure the connector works fine before reflow.

I did a study on the connector and found it was caused by the connector itself while through SMT high temperature reflow process as below two reasons:

Metal dome with dimple as keypad solution

Last article I mentioned that my company applied the metal dome without dimple as keypad contact solution just like the cell phone but we met keypad press insensitive  issue. Now we had solved the problem by adding the dimple back to the metal dome and still reach 1,000,000 times of finger press cycle lifetime.

We did some failure analysis and found the keypad insensitive defect was caused by two major issues. One is the foreign contamination, include dust and fiber, that I mentioned at last article. Another one is the oxidation show on the immersion gold finished on the ENIG board pads.

We found the oxidation particles look like the chemical of “P” exuded from base material of PCB. The “P” is one of the major element for the ENIG fabrication process. So we only can control less “P” but can’t remove it from the board.

Without dimple Metal dome as keypad contact

Recently we phased in the meal metal dome as rubber keypad contact solution. The same solution implement to many cell phone keypad solution also. The good is that metal dome can sustain 2,000,000 times of finger press lifetime verse 300,000 times for polydome.

Hot-Bar Flex cable Design Notices

The Hot-Bar reflow is a selective soldering process where connect two pre-fluxed, solder coated parts by heating element, call a thermode, with proper temperature to melt the solder.

Applying a pressure and contacting on the soldering target is necessary to melt the solder and insure that components stay in place during cooling.

Shipping carton drop/impact test

The electronic industry grows quickly. Each vendor takes responsible to his own component only to make it good and low cost. Take a flashlight manufacturer as example. There are bulb, wires, switch, spring, and plastic or metal housing make up the flashlight. The manufacturer buys all the sub-components from each supplier and assembles them together to fabricate the flashlight then sell to end-user.

All the sub-components are delivery by air, ocean, or truck to destination. It is important to prevent the delivery parts without damage during transferring. Most of the packaging uses corrugated paper carton and cardboard to hold inside components and prevent it from damage by falling or throwing down by porter or carrier.

Flex cable(FPC) Trace Pattern Layout Design Notices

Many FPCB designer are not familiar with the manufacturer and bring lot of quality issue after mass production. Here I summary some of the design notices for the flex cable (FPCB)  manufacturing  ability to prevent future quality fail.